What is Mr. Spacely's first name?

Mr. Spacely’s first name is Cosmo.

Cosmo G. Spacely is George Jetson’s short-tempered employer and the president of Spacely Space Sprockets. He routinely contacts George by videophone, usually beginning with a furious shout of “JETSON!” His company manufactures futuristic products built around the deliberately vague idea of “sprockets.”

Spacely is more than a one-note villain. Although he is greedy, impatient, and quick to threaten George’s job, he occasionally helps or sympathizes with him. His behavior is a running joke: George may be fired over a trivial mishap, only to be rehired before the episode ends.

A common mix-up is confusing Cosmo Spacely with Spencer Cogswell, his business rival. Spencer is the first name of Cogswell, who owns Cogswell’s Cosmic Cogs. Cosmo is also the name used for Spacely in later Jetsons productions and character references.