Before...
He grew up as an Aztec boy, over 500 years ago in Mexico. His community thrived inwhat is now modern day Chiapas, Mexico. He lived a happy normal life. It, of course, had its fair set of challenges, but he still thrived and was well taken care of. He was well mannered. Never did he dare to to speak when not spoken to, or do something he was not told to. He was a tresure in his household because of this.
Everything went downhill the day he drowned. All he wanted was some good, honest fun with his friends. But Tetzalipoca must have been laughing at him that day.Slowly he sank to the bottom of the lake, his life flashing before his eyes. His necklace, the jaguar amulet his mother, is what presumably saved(?) his life. It is unclear whether he survived or if he was killed and it just resurrected him. Nonetheless, it didn't matter. He was still alive.
Death?
He's true name was lost to time. Many still speculate that he does indeed remember it and just does not want to reveal it. Who knows. His amulet caused him to change, giving him the features of the sacred cat that it was shaped in. His hair, eyebrows and eyelashes slowly began to turn blonde, but slowly was bleached due to the salt of the lake and being under its water for centuries. His eyes turned a stark red. He gained...abilities after a while, too.
Life after--wait, he's not dead?
Myths of a humanoid jaguar began to circulate around Chiapas. Unsure of where it came from, it caught the attention of many people, some even reverting to worshiping it like a deity.
He lives a solitary life. He still clings to the memories he once had, still traumatised by the thing he had become all those years ago.