Eugène Delacroix painting pictures of nature in often violent action that are somewhat frightening, but nothing frightening about him as a person.
Perhaps you are thinking of another great artist Michelangelo Merisi da Caravaggio. He had lots of reasons to be feared.
Caravaggio led a tumultuous life. He was notorious for brawling, even in a time and place when such behavior was commonplace, and the transcripts of his police records and trial proceedings fill several pages.
Caravaggio left Milan for Rome in mid-1592, in flight after "certain quarrels" and the wounding of a police officer.
On 29 May 1606, he killed a young man named Ranuccio Tomassoni over a tennis game.