sidekick

noun2

1. •
   (informal) An assistant to another person, especially to a superior or more important person.

   • If representation and recruitment is an objective, self-styled mavericks like Kelly and his Queensland sidekick George Christensen have some utility. — 2021
2. •
   (figurative) 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. — 2023