mid-15c., "an athlete" (mid-13c. as a surname, Johannes le Gamer), agent noun from game (v.). Meaning "one devoted to playing video or computer games" is attested by 1981 (by 1975 in reference to players of Dungeons & Dragons). Gamester is attested from 1580s but also sometimes meant "prostitute" (compare old slang The Game "sexual intercourse" (by 1930s), probably from the first game ever played "copulation"). From 1550s as "a gambler." Gamesman is from 1947.
Quite a few of the gamers we've encountered during our monthly strolls down "Arcade Alley" suffer the same chronic frustration: finding enough opponents to slake their thirst for endless hours of play. [Video magazine, May 1981]