Sidekick
In literature, a sidekick was the hero's companion and aide.

While playing The Adventures of Captain Proton in 2375, "Demonica" (Jenny Delaney) informed "Captain Proton" (Tom Paris) that his "trusty sidekick" ("Buster Kincaid", aka Harry Kim) was indisposed. ()
Literary devices
The Adventures of Captain Proton
Occupations