Is there a name for characters who are not exactly part of the movie but affect the incidents in the movie?

Question

In some of the movies I have watched, there are some characters whose screen presence is less and has a minor role in the movie. But their role play an important role in causing a twist in the movie.

Below are the instances:

1. Thief who steals iron in the movie Express Raja. In the beginning of the movie, A voice over says

   This guy has nothing to do with movie but his actions play a major role in the movie.

2. M.S Narayana in the movie Devudu chesina Manushulu.

   From the wiki page of the movie,

   Panileni Papayya (M. S. Narayana) sits at a shop, eats a banana & throws the peel on the road.

   Due to this peel series of incidents happen and

   It ultimately leads to the quarrel of hero and the heroine.

   Unhappy with the outcome of the result, Goddess Lakshmi goes to past and makes the character to throw the banana peel in a dust bin. Due to this action, all the incidents change.

   But it ultimately leads to the same outcome where hero and the heroine quarrel.

So, Is there a name for such characters who has a minor role but affects the incidents/outcome of the movie?

Answer 1

Sound like Plot Device to me:

A plot device is an object or character in the story whose purpose is purely to drive the Plot, maintain its flow, or resolve situations within it.

Answer 2

Not exactly a name, but there does seem to be a trope for what you describe. I found Small Role, Big Impact on tvtropes.

Small Role, Big Impact is when a minor character (an "Under-Five" line player, as they used to say) who, through his or her actions or words, has an impact on the story far, far beyond what such a minor character ought to have normally.

Answer 3

Reading your comment to the other answer, I thought this might be an example of Stunt Casting

Hiring of a big-name actor to play a supporting role (or even a leading role, but usually the former). The idea is usually that the actor's fame will draw in viewers, as it normally would if you put them prominently on the advertising; but you don't have to pay them as much if they only have to do a few days' work.

Alternatively, it could be considered Billing Displacement

The tendency of a film to be retroactively linked in the public mind with the biggest name in the film or be marketed as "starring" the biggest name, even if that actor is not the main character (at least from the filmmakers' point of view), and occasionally even if his or her character is very minor indeed.

However, the two aren't mutually exclusive