sadist (n.)

"love of cruelty," especially as evidence of a subconscious lust that the cruelty satisfies, 1888, from French sadisme, from the name of Count Donatien A.F. de Sade (1740-1815). Not a marquis, though usually now called one, he was notorious for the cruel sexual practices described in his novels.

word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.

Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.

also sadomasochist, "one afflicted with sado-masochism," 1919; from combining form of sadist + masochist. Attested in German from 1913. Related: Sadomasochistic; sado-masochistic. Earlier was sadistic-masochistic (1892).