Originally a pet form of John, but now a well‐established given name in its own right. It is derived from Middle English Jankin, later altered to Jackin, from Jan (a contracted form of Jehan ‘John’) + the diminutive suffix -kin. This led to the back-formation Jack, as if the name had contained the Old French diminutive suffix -in. It is sometimes also used as an informal pet form of James, perhaps influenced by the French form Jacques. It has been the most popular boys' name in England and Wales since 1995. Well-known bearers include the actor Jack Nicholson (b. 1937) and the golfer Jack Nicklaus (b. 1940). See also Jock and Jake.