A down-and-out in Depression-era New York who meets the delirious Dr McCoy in 1930 and accidentally disintegrates himself with the doctor's stolen phaser.
The man known in the script as Rodent appears in the first-season episode The City on the Edge of Forever. He is first seen stealing a bottle of milk from a doorstep, at the moment McCoy, crazed by an overdose of cordrazine, comes through the Guardian of Forever into the street.
McCoy seizes him, raves about barbaric medicine and then collapses. The tramp goes through his pockets and comes away with a hand phaser. Alone in an alley, he turns it over, presses something and vanishes in a flash.
The incident passes unremarked, although it sits oddly with the story's concern that one death can change history. Rodent was played by John Harmon.