Vaccine Man is a villain from One Punch Man, being the very first villain Saitama faces in the series. He appears as a humanoid naked demon with blue skin and two antennas.
Vaccine Man shows up causing mass destruction, leveling up an entire city with his powers. When he's about to kill a child, Saitama shows up and save the kid. Vaccine Man claims he was born from the desires of Mother Earth, and that humans are a disease which is killing the planet and must be eradicated. He gets enraged when Saitama tells he is a hero just for hobby, transforming into a more demonic form and attacking Saitama, who pulverizes him with a single punch. He has a more similar appearance with Piccolo by Dragon Ball