There are numerous examples, but the character Jerry clearly sometimes enjoyed nudging his friends in various nefarious ways that would get them to act amusingly. In one episode, we learn that Elaine is so vehemently pro-choice she refuses to patronize a restraurant owned by a pro-life businessman. Later, she meets a new guy and becomes smitten with him, whereupon Jerry, on hearing of how perfect and great the guy is, casually inquires as to what the guy’s views on abortion are.
He’s just making trouble. It often seems like he keeps these people around him so he can get them to dance for his amusement. There must be other characters like this out there, but I can’t think of any. Who else in fiction is an instigator for the sake of their own amusement?
I think the master “troll”, in your sense of the word, would be the evil Mrs. Danvers from the Daphne DuMaurier novel / Alfred Hitchcock film “Rebecca”. The way she convinced our young sweet innocent heroine to wear the same fancy dress costume as the dead Rebecca - shocking, shocking I tell you! And the look on Max DeWinter’s face! I will never ever forgive her.
Rhea, from Stephen King’s Gunslinger series. She started shit just for the sake of starting shit, because she wanted to see the ensuing hullabaloo. And man, did she ever take it far.