Translation guide
A character in a story, film, game, etc. who is not a main focus; often appears in the background or has a minor role.
A character with a small role, not central to the plot.
Literally 'side role'. The most common term for a supporting or minor character in a story, play, or film.
He always plays minor roles.
A very small or bit part, often with few lines. More specific than 脇役.
The actor appeared in the movie in a bit part.
From 'mob character'. Used in anime/manga/game contexts for background characters with no individual identity.
The background characters in this game all have the same face.
A person appearing in the background of a scene, often without lines.
A character so minor they are not given a name or development.
Literally 'nameless character'. Used when a character has no name or is treated as insignificant.
A nameless character was suddenly killed.
Means 'the rest of the many' or 'the crowd'. Refers to a group of unimportant characters collectively.
Everyone besides the main character is just part of the crowd.
脇役 is a supporting role that may still have some importance, while 端役 is a very minor role with little to no impact on the story.
Avoid directly translating 'background character' as 背景のキャラクター. While understandable, it sounds unnatural. Use the terms above instead.
That background person is just standing there the whole time.