Rattler

Gustav Krueger is a mercenary who joined the Serpent Society, a professional syndicate of snake-themed villains, as Rattler — a formidable combatant equipped with a powerful cybernetic rattlesnake tail that he wields as both a weapon and a physical asset in battle.

Rattler slithered onto the scene in 1985's Captain America #310 — a Bronze Age Marvel debut courtesy of Mark Gruenwald and Paul Neary — and has been coiling through the Marvel Universe ever since, racking up appearances across four decades and three key collector issues along the way. A card-carrying member of both the Serpent Society and A.I.M., this villain runs in genuinely dangerous company, sharing pages with the likes of Captain America himself, Anaconda, and Blanche Sitznski across titles ranging from Captain America to The Amazing Spider-Man and Battle Scars. Gruenwald's Serpent Society era is rightly celebrated as one of Marvel's great villain-ensemble experiments, and Rattler is a bona fide piece of that legacy — not a headliner, perhaps, but a persistent, recognizable presence whose 33 catalog appearances prove real staying power. For collectors chasing that classic mid-'80s Cap continuity, Rattler is exactly the kind of deep-cut character who rewards the dig.