The good thief, as he is commonly referred, is an unnamed character who appears in all four Gospels—though it’s his interaction with our Lord in the Gospel of Luke that’s made him famous. Though he’s never been officially canonized by the Church, he is believed to be a saint by virtue of Christ’s words, “Truly, I say to you, today you will be with me in Paradise.” So I suppose you could say he was canonized preemptively by the Lord himself! He is traditionally referred to as St. Dismas and his feast day is March 25th.