Jiren the Gray. Not even Goku in Super Saiyan Blue could beat him.

 

"It matters not how many weaklings band together.
YOU ARE NOTHING before absolute strength"

Jiren is the only antagonist who isn’t a villain. He is currently the strongest being Goku’s ever fought, as seen in recent episodes of Dragon Ball Super. Jiren's existence was considered a rumor in other universes; he’s considered the only mortal that a God of Destruction cannot defeat. Jiren has a staggeringly long list of incredible feats.Jiren's presence unleashed such intense Ki it shook the entire World of Void, a realm of infinite size. He’s beaten every form in Goku’s arsenal easily, deflected Goku’s Universe 7 Spirit Bomb with just a glare, and broke out of a time prison by flexing, with an observation made that Jiren’s power transcends time itself. He’s even defeated Goku’s Ultra Instinct form, a form Gods of Destruction cannot utilize. At this rate, there’s nothing and no one who can defeat Jiren.