tin god

noun

1. a self-important, dictatorial person in a position of authority, as an employer, military officer, critic, or teacher.
2. a person who considers himself or herself infallible and tries to impose judgments, beliefs, standards of behavior, etc., on subordinates.

noun

1. a self-important dictatorial person
2. a person erroneously regarded as holy or venerable

A self-important, dictatorial, petty person who imposes ideas, beliefs, and standards on subordinates. For example, The officials in these small towns often act like tin gods. The tin in this expression alludes to the fact that tin is a base metal with relatively little value. [Late 1800s]