The "Gas Man" is a middle section survivor of Oceanic Flight 815.

On the Island

Day 1 (Season 1)

The "Gas Man" appeared during the initial aftermath of the crash, and walked past a screaming Shannon. He was yelling "Stay away from the gas!" to warn fellow survivors the dangers posed by it. ("Pilot, Part 1") ("Exposé")

He has not been seen since "Pilot, Part 1" and was last seen near the location of the wing, which subsequently collapsed and exploded. If the "Gas Man" had not died prior to the beginning of time shifts, then he died in the flaming arrow attack in 1954, ("The Lie") since Rose and Bernard Nadler are presumed to be the only survivors of it. ("The Incident, Part 1")