A sadist is a person that enjoys inflicting pain on others, the term is coined from the Marquis De Sade http://en.wikipedia.org/wiki/Marquis_de_Sade
There is also an interesting romanticized movie inspired by his life, "Quills" http://www.imdb.com/title/tt0180073/
A masochist is a person that enjoys receiving pain, there is some dispute as to whom exactly inspired this word but most people tend to believe Gilles De Rais is to blame http://en.wikipedia.org/wiki/Gilles_de_Rais
Together you have "sadomasochism" which is a person that of course enjoys receiving and inflicting pain. These terms are common in the BDSM world http://en.wikipedia.org/wiki/BDSM
Hope this helps!
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Noun: A sadist is someone who obtains pleasure from inflicting pain on others.
Source - Merriam-Webster - The Free Dictionary