Supporting character
CHARACTER IN A NARRATIVE THAT IS NOT FOCUSED ON BY THE PRIMARY STORYLINE
Supporting role; Side character
A supporting character is a character in a narrative that is not the focus of the primary storyline, but is important to the plot/protagonist, and appears or is mentioned in the story enough to be more than just a minor character or a cameo appearance. Sometimes, supporting characters may develop a complex backstory of their own, but this is usually in relation to the main character, rather than entirely independently.