According to Wikipedia:
Historically, Jesus was crucified along with two others, though only Luke describes one of them as penitent, and even that gospel doesn't name him. Luke's unnamed penitent thief was later assigned the name Dismas in the Gospel of Nicodemus, often dated to the 4th century. The name of "Dismas" was adapted from a Greek word meaning "sunset" or "death."[5] The other thief's name is given as Gestas. In Jean Joseph Gaume's Life of the Good Thief (Histoire Du Bon Larron French 1868, English 1882) the thief said to Jesus, the child: " O most blessed of children, if ever a time should come when I shall crave Thy Mercy, remember me and forget not what has passed this day."[1][2][3] Blessed Anne Catherine Emmerich saw the Holy Family "exhausted and helpless"; according to St. Augustine and St. Peter Damian, the Holy Family met Dismas, in these circumstances.[6]
The apocryphal Arabic Infancy Gospel calls the two thieves Titus and Dumachus, and adds a tale about how Titus (the good one) prevented the other thieves in his company from robbing Mary and Joseph during their Flight into Egypt.
In the Russian tradition the Good Thief's name is Rakh (Russian: Рах).
