Ja’far, The Liar (Kazzab)
Ja’far, generally known as Kazzab, was the son of Imam Ali Naqi (a.s.) and the brother of Imam Hasan Askari (a.s.). Since he had claimed Imamate against Imam Mahdi (a.j.), the biographers refer to him as Kazzab (liar). He was initially a wayward and an evil person. He had left no stone unturned in his enmity to Imam Hasan Askari (a.s.). He did not give up trying to get the Imam (a.s.) imprisoned, though he always failed in his efforts.
Regarding Ja’far Kazzab and his son, there is a saying of Imam Mahdi (a.j.) that they are like the brothers of Yusuf (a.s.). Tabarsi and some other scholars are of the view that Ja’far had repented like the brothers of Yusuf (a.s.) and that after this repentance, he came to be known as Ja’far Tawwab (Ja’far the repentant). This is also supported by the tradition of Riyazush Shahadat.