one-man show

Also, 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]