Arthur Fleck, later known as Joker, is a failed comedian who, following his great lack of success and respect, loses his mental stability until he becomes a nihilistic, sociopathic killer calling himself Joker, aiming himself to make Gotham smile in his way.
There are roughly one-sh*t billion tropes so PLEASE look through them before adding one. Otherwise add what you like. ADDITION: PLEASE read through the trope description provided before submitting something. It's not a huge deal but too often people submit characters that don't fit just because they misinterpreted the title...
