what do you call a character in a movie that serves no plot purpose but just as a prop for audience to laughat?

Like when the casting crews recruit characters with autism, serious
obesity, extremely unattractive characters as background props just to
exploit them in comedy (for example). They don't get say much or do
much in the story but just there so the audience could belittle them,
at least in their minds.

Is there a phrase or cliche to describe what these useless characters
are ?