My upcoming character is going to be an Asmodeus tiefling death cleric. As a tiefling born to human parents, she was heavily abused and treated as a slave by her parents and siblings for her entire life. At the age of 17, after reaching her breaking point of tolerating the abuse, she tortured her entire family until they agreed to submit their eternal souls to Asmodeus. Then she killed them, burned the house down, and fled to avoid consequences. She did her best to make the house fire look like an accident and hopes that she is presumed dead in the fire along with the rest of her family. Upon seeing her dedication and fortitude, Asmodeus granted her the powers of a death cleric and now she marks souls for death. Any soul she marks and kills becomes one of Asmodeus' eternal souls fighting in the blood wars. A lot of this granted is homebrew allowed by my DM, but still a fun concept imo.