For the lifeform nicknamed "Tin Man", please see Gomtuu.
The Tin Man was a character from the Earth story The Wizard of Oz; a mechanical man made of tin who longed to be Human. His lamentation of not being Human was expressed in the tune If I Only Had a Heart.
By the end of the story, he learned that he was always Human. He did not realize this as he worried so much. (TNG: "The Schizoid Man")
In the episode, Dr. Ira Graves only referred to the character as a mechanical man.