Before indulging in research on the aspects of Imam al-Jawad's personality and talking about his life and other related concerns, I would like to refer to his noble lineage and that which is associated with it, concerning his birth, his qualities and other things which might be considered as clues to talk about his personality.

HIS NOBLE LINEAGE
In the world of lineages, there is no lineage nobler or more exalted than the lineage of Imam Abu Jafar al-Jawad (a.s). He was from the heart of the Prophet’s family, which was the holiest, most honorable family that humanity has ever known throughout the ages, the family that has provided the world with the elements of virtue and perfection and illuminated all the corners of life with knowledge and faith. The honored origins and pure wombs he came from are as follows:

HIS FATHER
His father was Imam Ali ar-Redha binImam Musa bin Ja’far al-Kadhim bin Imam Muhammad al-Baqir bin Imam Ali Zaynol Aabideen bin Imam al-Husayn bin Imam Ali bin Abu Talib (peace be upon them). This is the golden chain which if read on the deaf and the dumb they will recover by the will of Allah, as al-Ma’moon, the Abbasid caliph, has said.Ahmed bin Hanbal says, “If this chain of lineage is recited on a mad person, he will recover from his madness.” 
Abul Ala’ al-Ma’arri,who mistrusted most people, said regarding this noble family,
“The ones whose brilliance was shown
before the creation of Mars and Libra,
before the Heavens had been created,
and their orbits had been ordered to circuit.”
From this good and noble tree, close to Allah and dear to every Muslim, Imam Muhammad al-Jawad (a.s) branched out.

HIS MOTHER
His mother was one of the purest and most abstinent and virtuous of Muslim women. It was sufficient to her that she had given birth to one of the best figures of Islam and one of the best imams of the Muslims. It did not degrade her position nor harm her dignity that she was a bondmaid. Islam has declared a war against this phenomenon and considers it as an aspect of the pre-Islamic life, which Islam has done away with. In the Islamic point of view, piety and obedience to Allah are the bases of preference amongst people and nothing else.
Islam proudly annulled all kinds of racial segregation and considered them as factors of backwardness and declination in society because they divided the nation into fighting sects and parties. Therefore, the imams of the Ahlul Bayt (a.s) married bondmaids in order to do away with malicious feuds and remove the causes of separation amongst Muslims. Imam Ali bin al-Husayn Zaynol Aabideen (as-Sajjad) (a.s) married a bondmaid who gave birth to the great revolutionary martyr, Zayd. Imam ar-Redha (a.s) married a
bondmaid who gave birth to Imam al-Jawad (a.s). The situation of the infallible imams in their marriages with bondmaids was a decisive refutation towards the enemies of Islam who tried their best to keep Muslims divided. 
As for the name of the mother of Imam al-Jawad (a.s), historians disagree, and each group says something different. Here are some of the historians’ accounts:
1. Her name was al-Khayzuran. Imam ar-Redha (a.s) named her so when her actual name was Durrah. 
2. Her name was Sukaynah al-Nawbiyyah, or al-Muraysiyyah , as was said by historians. It was said that her lineage belonged to Maria al-Qubtiyyah the wife of Prophet Muhammad (a.s). 
3. Her name was Rayhanah. 
4. Her name was Sabeekah. 
Some sources of history neglect mentioning her name and just call her “Umm Walad.”Anyhow, it is not of great importance to know what her actual name was. Of greater interest is her life history; however, unfortunately, the sources at hand have not mentioned anything about her life.

THE GREAT NEWBORN
Imam ar-Redha (a.s) took much care of his (wife) bondmaid because he had perceived through the unseen that she would give birth to a boy that Allah had chosen for the imamate and the general guardianship of the Holy Prophet (a.s). He would be one of the Prophet’s twelve successors. Imam ar-Redha (a.s) had informed his close companions of that.
Imam ar-Redha (a.s) entrusted his honored sister Hakeemah bint Imam Musa bin Ja’far al-Kadhim (a.s) to remain with his wife until she gave birth to her child.Lady Hakeemah carried out everything her brother had asked her to do. When the bondmaid felt she was about to give birth, Imam ar-Redha (a.s) asked his sister to come with a midwife. Imam ar-Redha (a.s) lit a lamp in the houseand remained in expectation of the great newborn. It was not long until his bondmaid gave birth to a great figure of intellect and jihad in Islam.

THE DELIGHT OF IMAM AR-REDHA (A.S)
Waves of delight and joy overcame Imam ar-Redha (a.s) after the birth of his blessed newborn son. He began saying, 
“The like of Moses son of Imran, the splitter of the seas, and the like of Jesus son of Mary, blessed be the mother that bore him… has been borne to me.”
Imam ar-Redha (a.s) turned to his companions and told them the good news of his newborn son. He said, ‘Allah has granted me one who will inherit me and inherit the children of Dawood….’
He told them that that newborn child would be the imam after him.He received that great newborn with tremendous joy and delight because that child was the awaited spiritual leader of the umma for that period. Amongst his companions, there was Di’bil al-Khuza’iy,a poet of the Ahlul Bayt (a.s). He participated with the Ahlul Bayt (a.s) in their joys and delights over the birth of Imam al-Jawad (a.s).

CEREMONIES OF THE BIRTH
Imam ar-Redha (a.s) took his newborn son and carried out the ritual ceremonies for him. He recited the adhan in his right ear and the iqamain his left ear and then placed him back in his cradle. 
HIS SURNAME
Imam ar-Redha (a.s) gave his son Imam Muhammad al-Jawad (a.s) the surname of Abu Ja’far, like the surname of his grandfather Imam Muhammad al-Baqir (a.s). It is differentiated between them by saying Abu Ja’far the first for Imam al-Baqir (a.s) and Abu Ja’far the second for Imam al-Jawad (a.s).

HIS EPITHETS
As regards his noble epithets, they show his great personality and exalted self. The most common are as follows:
1. Al-Jawad (the generous): he was thus called because of his abundant acts of good, beneficence and charity towards the people.
2. Al-Taqiy (the pious): he was thus called because he feared Allah and turned and resorted to Him. He never responded to any incitement of desire or fancy. Al-Ma’moon, the Abbasid caliph, had tried him with different types of provocations, but he was not deceived. He turned to Allah and preferred His obedience to anything else.
3. Al-Qani’ (the satisfied).
4. Al-Murtadha (being satisfied with). 
5. Al-Radhiy (the satisfied).
6. Al-Mukhtar (the elect).
7. Al-Mutawakkil (the reliant (on Allah)).
8. Al-Zakiy (the pure). 
9. Bab al-Murad (the gate of desires and hopes).He was known by this epithet amongst the Muslims who believed that he was a gate from the gates of the Divine Mercy, to which afflicted and needy people resorted in order to rid themselves of their misfortunes and afflictions.
These are his epithets of which each and every one refers to one of his exalted qualities and noble tendencies that are a source of pride to this umma.

HIS FEATURES
His features were like those of his fathers, which in turn were like the features of the prophets. The lineaments of piety were apparent on his holy face. Some sources of history describe him as “white-faced with a moderate stature.”Other historians mention that he was very brown based on only one odd narration,which Imam al-Khoo’iy proved to be a fabricated narration.We have therefore brushed this narration away for it is odd and untrue.

HIS BIRTHDAY
Historians widely concur that Imam al-Jawad (a.s) was born on the nineteenth of Ramadan, 195 AH.It has also been mentioned that he was born on the fifth of Ramadan, 175 AH, but this is totally untrue for it is
definite that he was not been born in that year but in the year 195 instead, as narrators and historians have unanimously agreed.

THE FIGURE ON HIS RING (SEAL)
The figure on his ring showed that he had devoted himself to Allah. He had written on his ring (as his own seal) “glory is (only) to Allah”.He believed that glory was to Allah alone, the Creator of the universe and the Giver of life.

HIS UPBRINGING
Imam Muhammad al-Jawad (a.s) was brought up in the house of prophethood and imamate, that house by which Allah had honored the Muslims. He grew up in the shade of that honored house while receiving high ideals from his father, who shed rays of light from his great soul onto him. His father himself had undertaken his upbringing. He took him with him wherever he went and fed him with his own hands. Yahya as-San’ani said, “Once, I went to Abul Hasan ar-Redha (a.s) (Imam al-Jawad’s father) in Mecca while he was peeling a banana and feeding Abu Ja’far (Imam al-Jawad). I said to him, ‘May I die for you! Is this the blessed newborn?’ He said, ‘Yes, O Yahya! This is the newborn that no one in Islam has been born for our Shia more blessed than him.’”
This kind of education coupled with love and respect has a great influence on the psychological structure and success of a person, according to psychologists and educationists.

HIS INTELLIGENCE AND GENIUS
Imam Muhammad al-Jawad (a.s) displayed signs of intelligence and genius in his early years that astonished people and filled them with admiration and high regard. Historians have mentioned many signs of his intelligence. Here are some of them:
1. Umayya bin Ali narrated, “I was with AbulHasan ar-Redha in Mecca in the year that he went on pilgrimage to bid farewell to the Sacred House (the Kaaba) when he intended to travel to Khurasan (in Iran). His son Abu Ja’far al-Jawad was with him. Abul Hasan bid his farewell to the House and went to the Sanctum (of Abraham) and offered prayer there. Abu Ja’far was carried by one of Imam ar-Redha’s servants to circumambulate the Kaaba. When he (with the servant) reached the Rock of Abraham, he sat there and remained for some time. Muwaffaq, the servant, asked him to get up so they could leave, but he refused and was very sad and depressed. Muwaffaq went to Imam ar-Redha (a.s) and told him about the state of his son. Imam ar-Redha (a.s) came and asked him to get up. He responded to his father with sighs and tears saying, ‘How can I get up O father, while you have bid farewell to the House in such a way as if you shall never come back to it…?’
A wave of pain occupied Imam ar-Redha (a.s). He begged his son to come with him and the son responded to his father.”
This event shows the intelligence of Imam al-Jawad (a.s) because he understood from the farewell of his father to the Sacred House that it was his last farewell. He saw the fear and grief in his father’s expressions that
made him perceive it was the end of his father’s life. Indeed it was so, because Imam ar-Redha (a.s), after his travel to Khurasan, did not come back to the sacred lands (Mecca and Medina). He was martyred at the hands of al-Ma’moon, the Abbasid caliph, with poison.
2. Once, al-Ma’moon with his official procession passed by some children playing in a street in Baghdad, amongst whom was Imam al-Jawad (a.s). When the children saw the procession of al-Ma’moon, they ran away except Imam al-Jawad (a.s) who remained standing in his place. Al-Ma’moon, who did not know this child, became astonished and asked him, “Why did you not run away with those children?”
Imam al-Jawad (a.s) answered with a wonderful reason that affected al-Ma’moon. He said, “O Ameerul Mo’mineen,the street is not so narrow that I should clear it for you and neither have I any guilt that I should fear you. I trust that you do not harm a guiltless one.”
Al-Ma’moon was astounded and asked the child about his lineage, to which Imam al-Jawad (a.s) responded accordingly. Al-Ma'moon prayed to Allah to have mercy on Imam al-Jawad’s father.We shall discuss this point later on.
3. One of the signs of his incredible intelligence is that when he was in his early childhood, scholars and jurisprudents asked him thirty thousand questions and he answered them all. There is no way to justify this phenomenon except to say that Allah the Almighty has endowed the Ahlul Bayt (a.s) with great powers of knowledge that He has endowed to no one except His Arch-prophets.

IMAM AR-REDHA PRAISES IMAM AL-JAWAD
Imam ar-Redha (a.s) always praised Imam al-Jawad (a.s) and pointed out his virtues and talents. Once, al-Fadhl bin Sahl sent to Muhammad bin Abu Abbad, the clerk of Imam ar-Redha (a.s), asking him about the kind of relation of Imam ar-Redha (a.s) with his son Imam Muhammad al-Jawad (a.s), and the clerk replied, “Ar-Redha does not mention (his son) Muhammad except by his surname. He often says: Abu Ja’far (Muhammad al-Jawad) wrote to me, or I wrote to Abu Ja’far…and even though he is yet a child in Medina, the letters that come to his father are so eloquent and fluent.”
Narrators have narrated of the extent that Imam ar-Redha (a.s) would glorify his son Muhammad al-Jawad. They said that once Abbad bin Isma’eel and ibn Asbaat were with Imam ar-Redha (a.s) in Minawhen Abu Ja’far was brought to his father ar-Redha (a.s). They asked him, “Is this the blessed newborn?”
Imam ar-Redha (a.s) became delighted and said, “Yes, this is the newborn that no one in Islam has been born more blessed than him.”
There are many other narrations related from Imam ar-Redha (a.s) showing that he often praised Imam al-Jawad (a.s) and pointed out his great talents and virtues.

GLORIFICATION
Imam al-Jawad (a.s) was surrounded, since his early days, with a halo of glorification and exaltation by the religious people who believed that he was
one of the Prophet’s successors, the love of whom Allah had imposed on all Muslims. 
Historians mention that Ali bin Ja’far, the great jurisprudent and the brother of Imam Musa bin Ja’far (al-Kadhim) (a.s) and one of the famous personalities of the AlawidFamily at that time, was one of those who sanctified Imam al-Jawad (a.s) and acknowledged his virtue and imamate. 
Muhammad bin al-Hasan bin Imara said, “Once, I was with Ali bin Ja’far in Medina, where I stayed with him for two years to write down what he had heard from his brother (Imam Musa al-Kadhim), when one day Abu Ja’far Muhammad bin Ali (al-Jawad) (a.s) came into the mosque of the messenger of Allah (a.s). Ali bin Ja’far suddenly jumped without shoes or garment and kissed his hand and glorified him. Imam al-Jawad (a.s) looked at him and said, ‘O uncle, sit down please! May Allah have mercy on you.’
Ali bin Ja’far bowed respectfully and said, ‘O my master, how can I sit while you are standing?’
Imam al-Jawad (a.s) went away and then Ali bin Ja’far returned to his companions. They began scolding him for glorifying Imam al-Jawad (a.s) who was very young yet. They said to him, ‘You are the uncle of his father, so why did you act in that way with him?’
He answered them with the answer of one who believed in his Lord and religion and who recognized the actual position of the imamate. He said to them, ‘Keep silent! It is Allah Who has not qualified this beard (he caught his beard with his hand) for the imamate and has qualified this young man and placed him in that position according to His will. We seek the protection of Allah from what you say. I am just a slave to him (to Imam al-Jawad).’” 
Ali bin Ja’far proved that the imamate did not submit to the wish of man or his will but was instead in the hand of Allah, Who chose for it whom He willed from amongst His people, regardless of whether the imam was young or old.

IMPRESSIONS OF HIS PERSONALITY
The talents of Imam Muhammad al-Jawad (a.s) occupied the passions of scholars, and they therefore recorded their admirations and glorifications of him in their books. Here is some of what they have said about him:
1. ATH-THAHABI
Ath-Thahabi has said, “Muhammad (al-Jawad) was surnamed al-Jawad (the generous), al-Qani’ (the satisfied) and al-Murtadha (been satisfied with) and he was one of the chiefs of the Prophet’s family…he was described as being generous; therefore, he was surnamed al-Jawad….” 
2. IBN TAYMIYA
He has said, “Muhammad bin Ali al-Jawad was one of the notables of the Hashemites. He was famous of his generosity, and, therefore, he was called al-Jawad.” 
3. AS-SAFADI
As-Safadi has said, “Muhammad (al-Jawad) was surnamed al-Jawad, al-Qani’ and al-Murtadha. He was one of the chiefs of the Prophet’s
family…he was described as being generous; therefore, he was surnamed al-Jawad….” 
4. IBN AL-JAWZI
As-Sibt bin al-Jawzi has said, “Muhammad al-Jawad followed the footsteps of his father in knowledge, piety and generosity.”
5. MAHMOOD BIN WUHAYB
Sheikh Mahmood bin Wuhayb has said, “Muhammad al-Jawad inherited the knowledge and virtue of his father, and he was the loftiest amongst his brothers in position and perfection.” 
6. AZ-ZARKALI
Khayruddeen az-Zarkali has said, “Muhammad bin ar-Redha bin Musa al-Kadhim, at-Talibi, al-Hashimi, al-Qurashi, Abu Ja’far, surnamed al-Jawad, the ninth of the twelve imams of the Shia, was exalted like his ancestors, intelligent, eloquent, quick-witted….’
7. KAMALUDDEN
Sheikh Kamaluddeen Muhammad bin Talha has said, ‘As for the virtues of Abu Ja’far al-Jawad, they did not last long for the Divine Fate had determined that he would stay in this world for a little while and leave for his Lord soon; so his stay was brief and his days were short.’
8. ALI BIN EESA AL-ARBALI 
He has said, ‘Al-Jawad was in all cases generous (jawad)…he exceeded all people in the purity of his lineage and birth and sat on the top of glory. No one had ever approached his rank or his glory. He was exalted in position. His high position was above stars and his rank was above all ranks. When a delegation saw a fire, they said: it must be his fire.No fire was predominant over his fire. Exalted was he towards highness. Glory and honor felt proud of him. Mastership found its meaning in him. He was far from every vice and close to every virtue. Nobilities diffused from his sides and glory dripped from him. News of generosity were narrated about him, his progeny and his fathers. Blessed is he who strives to be loyal to him, and woe unto him who tries to be his opponent. When the loots of glory and loftiness are divided, the purest of them will be his, and when the backs of honor are mounted, the highest of them will be his. He matches the rain in generosity and the lion in courage and zeal and defeats conducts with his good conduct.’

Taken from Baqir Sharif Qarashi's Book: http://alhassanain.org/english/?com=book&id=123