Supporting character

A supporting character is a character in a narrative that is not the focus of the primary storyline, but 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. In television, supporting characters may appear in more than half of the episodes per season.
In some cases, especially in ongoing material such as comic books and television series, supporting characters themselves may become main characters in a spin-off if they gain sufficient approval from their audience.