1580s,Harlicken, one of the stock characters of Italiancommedia dell'arte, from ItalianArlecchino or one of its variants (Arlechin, Arlechì,etc.)

A 19c. theory proposes it to be from Old FrenchHerlequin,Hellequin, etc., leader ofla maisnie Hellequin (the household of Hellequin) a troop of demons who rode the night air on horses. The English form of the name isHurlewain.

However, the earliest depictions of Harlequin show him as a crass and bumbling servant character, rather than as a magical hero (as he had become in 19c. pantomime) which raises doubts about this proposed origin. The character is first recorded in a French text, but among other Italian characters, making an Italian origin not unlikely.More here.

From his ludicrous dress comes the English adjective meaning "particolored" (1779).