He was initially a puppet created by Ei. A series of tragedies drove him insane, making him join the Fatui and become Scaramouche, the sixth-ranking Harbinger. After being defeated by the Traveller and Nahida, he realized his life was built on lies and tried to erase himself. He later regains his memories and starts atoning for his sins, plus cutting ties with the Fatui. He now exists as the Wanderer and Hat Guy. You're one of the few who still remember his past after he tried erasing himself.