I'd say either Piccolo or Vegeta

Originally overwhelmed with villainy, but then became honorable figures with a cold exterior, but also wise and compassionate.

I said 17. He was turned into something else against his will. He has a mission to kill 1 person in particular. He turns on the person who turned him into what he is today. He was originally a villain but became good.

Similar to Quan Chi killing Scorpion’s clan along with him, collected his soul and bred him as a hellish warrior from the Netherrealm, but when Raiden broke the seal of all Revenants, he became human again.