the joker

"the joker is a homicidal maniac with a clown-like appearance who takes comedic delight in violent crime, creating chaos and challenging batman. he is generally acknowledged to be batman's arch-nemesis and worst enemy, gleefully citing the relationship between the two as being comedy and tragedy, disorder and order, two sides of the same coin."

(bkz: heath ledger)
(bkz: the dark knight)
(bkz: why so serious)