Ethan Namakura

Ethan Namakura is a son of Nemesis who served as a henchman of Kronos in the Titan Wars. He betrayed Kronos before and fell into Olympus. Then he was reborn as the Robo Rebel.

Percy Jackson series
Before that he was a demigod captured by The Titan army. Then he brought back Kronos and served him and betrayed him and died.

Son of Neptune Rebooted
He was reborn as The Robo Rebel and became pure evil.