Haegolbyeongsa

He is a skeleton who has the ability to return to a specific point in time every time he dies.

Skeleton was just a regular Skeleton Soldier minion placed under the Demon Lord Baal. His past as a human remains unknown. His grave where his remains are buried had no clues about his past. The tombstone of his grave had been scratched so bad that they can't even see his name on it.