Henry was a Glader who's name was seen engraved on the wall of the Glade in The Maze Runner film. His name was not crossed out at the time, therefore he was alive when Thomas arrived. It is unknown what he looks like and is never mentioned. Henry is presumed to have died during the Griever attacks or, if he had survived and was Immune, to have escaped to the Safe Haven in The Death Cure.
Henry name

Henry's name as seen engraved on the wall