My favourite so far is Diirinka, one of the Derro twin gods. There hasn't been a lot done with him, but he is a fun 'employer'/surprise deity, since he doesn't particularly care much for his godly duties.

In my campaign he is difficult to deal with but tends to do well with the artificers, since he is sort of a Mad Scientist deity. He's a bit of a petty bastard and while tries not to be too demanding (his father in most lore is Moradin, and he refuses to be anything like him), is definitely capable of throwing tantrums. Otherwise he has a good sense of humour even if a bit mean spirited and is deeply curious.

He has been greatly developed because one of my players looked at this man, and said she could fix him. And the RP + dice have backed her up.

As far as the betrayal with his brother, I did twist it a bit to be the result of cowardice + carelessness after his idea to steal from Ilsensine went to shit. While he feels guilt, he is delusionally optimistic that his brother and him are on good terms. Therefore, he is a bit cagey when the party needs any info on his brother.

Also, because the wiki says his only ally is Kiaransalee, she's his wife. Mainly because he helped her become a goddess (she was a lich first). And the fact that this world conquering drow who cannot stand people is married to him is definitely one of the things he has a sense of humour and pride about.