all four Gospels state that two men were crucified with Jesus;
Mark and Matthew state that both men mocked Jesus;
Luke alone states that one mocked but the other defended Jesus;
no canonical Gospel names either man.
The two accounts (two mocking; only one mocking) are inconsistent;
the name "Dismas" has no scriptural basis;
"Dismas" makes sense as a story of a repentent thief but not as a confirmed historical event.