sidekick

noun

Etymology: From side + kick, which in the late 19th and early 20th century was a slang term for the front side pocket of a pair of trousers, known as the pocket safest from theft. Thus, by analogy, a "side-kick" was a person's closest companion.

1. An assistant to another person, especially to a superior or more important person.

   “In the abstract, Stuhlbarg’s twinkly-eyed sidekick suggests Joe Pesci in Lethal Weapon 2 by way of late-period Robin Williams with an alien twist, but Stuhlbarg makes a character that easily could have come across as precious into a surprisingly palatable, even charming man.”

   “If representation and recruitment is an objective, self-styled mavericks like Kelly and his Queensland sidekick George Christensen have some utility.”

2. In literature, theatre, etc., a good foil of the protagonist, a character who helps emphasize the traits of the main character.

   “So even though he had – no question – the best lines in Friends, he was never what he would have been in an earlier era: the sidekick.”