Someone or something that is benign is gentle, kind, mild, or unharmful: a benign soul wouldn't hurt a fly.
Benign describes a range of qualities, all of them positive. When talking about a person, it means "gentle." In reference to weather or climate, it means "mild." In some other contexts, it simply means "not harmful"; you might speak of "a benign tumor" or "an environmentally benign chemical." The word comes from a Latin root benignus meaning "well born," but the implied meaning is "kind" or "pleasant" — it's hard to get mad at someone who has a benign disposition.