Judas is an unlockable character in The Binding of Isaac. He is unlocked by completing The Womb or Utero for the first time.
"Judas' Fez" - Defeat Mom's Heart once.
"The Robo-Baby" - Kill Mom's Heart with Judas.
"The Monster Manual" - Kill Satan with Judas.
"The Curved Horn" - Kill Isaac with Judas.
"Judas' Tongue" - Kill ??? with Judas.