A person who is multi-talented. Usually very silent, because of the constant thinking their mind is undergoing. Often mistaken for a hermit, a schizoid, or pretentious. A trait that a Rosemar would have is curiosity and a tendency to quote many famous philosophers.
If I had known you had such a knack for knitting, writing, kayaking, scuba-diving, card games, and pole vaulting, I would have said you were a Rosemar.