Garou

Abilities:

[Spoiler] Superhuman Physical, Prowess, Supernatural Senses, Afterimage Creation, Accelerated Development, Indomitable Will, Technique Mimicry, Regeneration [/Spoiler]

He was the best disciple of Bang's dojo, until he went on a rampage against the other students and disabled many of them for life. He was expelled after getting a beating by Bang.

[Spoiler] He eventually becomes the strongest villain, ranked as a Dragon+ level threat (considered around the same strength as Boros). Using his "God-Slayer Fist," he easily defeats Golden Sperm and most of the remaining S-Class heroes. In an epic fight with Saitama, the man is ultimately defeated but manages to escape before the heroes are able to get rid of him for good. [/Spoiler]