What was the name of the first episode to feature Harry Mudd?

The first episode to feature Harry Mudd was "Mudd's Women." It is the sixth episode of Star Trek: The Original Series and introduced Roger C. Carmel as the flamboyant interstellar con man.

In the story, the Enterprise pursues an unregistered cargo ship and rescues Mudd along with three women he is transporting to become wives for settlers. Mudd presents himself as a businessman and broker, but his schemes depend on deception, manipulation, and a mysterious beauty treatment. The episode combines a romantic premise with a science-fiction explanation for the women's unusually attractive appearance.

"Mudd's Women" first aired on October 13, 1966. It was written by Stephen Kandel from a story by Gene Roddenberry and directed by Harvey Hart. The episode also creates an early technical crisis for the Enterprise: protecting Mudd's ship damages the engines and leaves the vessel with only one functioning lithium-crystal circuit.

Mudd later returns in the second-season episode "I, Mudd," which is why that title is an especially tempting wrong answer. "The Menagerie" and "The Trouble with Tribbles" are also original-series episodes, but neither introduces Harry Mudd. He later appears in the animated series and in Star Trek: Discovery.