An eponym based on Count Donatien Alphonse Francois de Sade (1740 - 1814) a French novelist whose books were full of sexual fantasies of torturing sexual partners.
De Sade was condemned to death in 1772 because of his writings, but escaped to Italy. His life was filled with unmentionable adventures until he was finally caught and locked up in the Charenton Lunatic Asylum. He died there in 1814.
Sexologist Kraft-Ebbing coined the term sadism in 1872. It currently is used to cover practices like bondage and dominance, along with 'torture' (or pseudo-torture). It is often lumped with masochism (another eponym), as in the terms sadomasochism and BDSM; these nodes have much more information.