Oh yeah, isn’t he the guy who collected the dragon balls and became the wizard king?

No, you're confusing him with Rimuru. He is the guy whose sister turned into a demon and is on a journey to find the One Piece.

Ah

I thought Rimuru was on a quest to find the Philosopher's Stone and kill all criminals

No, that's Tohru, the one who's going to become the greaatest hero in the world