Noun for someone fun and caring and compassionate

Although mensch is good, the person being called that will probably need a dictionary or they might punch you. I prefer a more common word, gentleman.

Perhaps a delight

great pleasure, satisfaction, or happiness, or something or someone that gives this

Another possibility is charmer

a person who is enchanting or delightful to be around

However, this latter term is sometimes used to signify one who is engaging but insincere.

Well, it's a Yiddish loan word: mensch comes to mind.

It means he's an honorable, good person, but it's taken on all sorts of other positive connotations since its importation to English.

It doesn't quite bring up the fun to be around part, though.

Used in the example sentence: Bob is a real mensch.

Otherwise, you would just call him a great guy. Which probably brings with it all of the connotations you were trying to express.

How about social butterfly or philantropist? (And one which could be used in a more colloquial context or as a nickname, which I just came up with is jokebox. Only half-serious suggestion... ;) )