Gunner participated on the Losers' mission in Operation Four Horsemen in rescuing Colonel Richard Flagg and his squad on the once uncharted Dinosaur Island. Upon violently arriving on the island, Gunner and the Losers were beset by a tyrannosaurus rex. Gunner quickly took action and used a bazooka in effectively harming the T-rex. But just as Gunner was reloading, the dinosaur thrashed it's tail at him. Which fatally broke his entire body. Gunner died instantly in front of his closest friend Sarge. Gunner was mourned by the remaining Losers and was personally buried by Sarge.
- 1 Appearances of Gunner MacKay (Earth-21)
- 2 Images featuring Gunner MacKay (Earth-21)
- Quotations by or about Gunner MacKay (Earth-21)
- Character Gallery: Gunner MacKay (Earth-21)