Toxic Chainsaw

Super Venom Chainsaw is a villain in Boku no Hero Academia. He critically injured All Might to the point that he was almost dying.

Personality
Nothing is known about his personality. However, since he is a villain and seen the reaction of someone who is knowledgeable about the heroes and villains it's most likely that he was ruthless and did horrible things as he is still feared till now.

History
Super Venom Chainsaw once fought against All Might 5 years before the actual storyline, this fight left All Might with a terrible injury.

He is still know by some people as shown when All Might mentioned him Izuku Midoriya reacted in fear and trembled.

Quirk
His Quirk is unknown, however, it's powerful enough to critically injure All Might to the point of almost dying and putting him in his current state.