An enterprise, business, etc, controlled by one person: The company had previously been run as a ''one-man show''(entry form 1921+, variant 1938+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with one-man show
one-man band. A person who does or manages just about everything, as in This department is a one-man show—the chairman runs it all, or John conducts the interviews, writes the articles, solicits ads, deals with the printer—he's a one-man band. This idiom alludes to the actor or artist responsible for the entire performance or exhibit, or the musician who plays every instrument in the group.
[ First half of 1900s