Who were Dismas and Gestas?

The names of the two thieves crucified with Jesus. Dismas, on Christ's right, repents and eventually joins Christ in Heaven, while Gestas blasphemes and ends up in Hell.

Saint Dismas (sometimes spelled Dysmas or only Dimas, or even Dumas), also known as the Good Thief or the Penitent Thief, is the apocryphal name given to one of the two thieves (Matthew 27:38) who was crucified alongside Jesus. Dismas was the thief who repented of his sins and asked Jesus to remember him in his kingdom.

The other thief's name is given as Gestas. The apocryphal Arabic Infancy Gospel calls the two thieves Titus and Dumachus, and adds a tale about how Titus (Dismas) prevented the other thieves in his company from robbing Mary and Joseph during their Flight into Egypt. In Russian tradition Good Thief's name is Rakh.

https://en.wikipedia.org/wiki/Dismas