Sources

https://www.wikipedia.org/

http://batman.wikia.com/wiki/The_Joker

http://dc.wikia.com/wiki/Batman:_The_Killing_Joke

http://www.imdb.com/character/ch0000180/quotes

Google Images

Disclaimer

This is a Highschool project I have no affiliation with DC Comics, The Batman television series or movie series.