Sidekick

A sidekick is "a close companion or colleague who is, or is generally regarded as, subordinate to those whom they accompany." The word's first recorded use is from 1896, and it did not, as sometimes claimed, originate as pickpockets' slang. In fiction the sidekick's functions are many: a counterpoint or alternate point of view, a supplier of skills or knowledge the hero lacks, comic relief or the straight man to a comic hero, an identification figure for the audience, a questioner who draws out exposition like a Greek chorus, and a confidant whose attachment makes a detached hero likable. The lineage runs from Enkidu and Sancho Panza to Dr. Watson, Robin and Spock.

For novelists the sidekick is the smallest ensemble unit: one subordinate relationship that gives the protagonist someone to talk to and to think against. Serial writers lean on the role hardest, because a built-in conversation partner carries exposition and varies the page. See managing an ensemble cast.