Who was Fred's boss at the Slate Rock and Gravel Company?

Fred's boss at the Slate Rock and Gravel Company is Mr. Slate.

Mr. Slate is usually identified as Nate Slate, although the series jokes that his first name changes from episode to episode. He is Fred Flintstone's short-tempered supervisor at the gravel pit, where Fred operates a bronto crane. Mr. Slate repeatedly fires Fred over workplace mishaps, only to rehire him—often with a raise after Fred complains.

The company itself is one of Bedrock's major employers. In the episode “The Long, Long, Long Weekend,” Mr. Slate is portrayed as its founder, and the business is shown surviving two million years into the future under a descendant named George Slate the Eighty-thousandth.

A minor source of confusion comes from early episodes, in which a supervisor named Mr. Rockhead appears while a shorter character is called Mr. Slate. The identities gradually switched, and Mr. Slate became the established name for Fred's boss.