Judah was the son of Jacob and Leah.  When his brothers wanted to kill Joseph, Judah proposed selling Joseph into slavery instead.  When Judah and his brothers later came to Egypt to buy food, Joseph did not reveal his identity to them.  Instead he charged them with spying and later with theft.  When Joseph said that Benjamin would be imprisoned, Judah offered to go to prison in his place.  At that point, Joseph made his identity known.