significant midget

A tiny but essential component in a complex system or a small but influential idea in a broader context.

"Although it may seem insignificant, the tiny screw that holds the gears in place is actually a significant midget in the functionality of the clock."

Here's another example sentence:

"Although he may not have been the main character in the film, the actor's powerful and emotional performance made him a significant midget in the movie's success."