Captain America’s shield is one of comicdom’s great “unbreakable objects.” That, of course, makes for terrific drama when something comes along that can break it. The Marvel Cinematic Universe has put it to the test a number of times – as well as flat-out destroyed similar items like Thor’s hammer – but What If…? Season 1 placed a definitive stamp on it. Not only did Episode 8, "What If... Ultron Won?," show Cap’s shield shattered, it confirmed which MCU Avenger could do it.

The shield is made of vibranium, a fictional element that's found almost exclusively in Wakanda and is responsible for that nation’s accelerated development and technology. It’s both lightweight and bulletproof, and can withstand virtually any punishment inflicted on it. Its only vulnerabilities seem to be other items made of vibranium or similarly super-hard elements. Adamantium, which is best known as what makes up Wolverine’s claws, is such an element. But while that doesn’t exist in the MCU (yet), there's someone else who serves a similar purpose in the episode's alternate reality.

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Which Marvel Characters Can Break Captain America's Shield?

Captain America (Chris Evans) lays unconscious next to broken shield in Avengers: Age of Ultron.

Throughout Marvel history, the breaking or shattering of Captain America's shield has been a potent visual shorthand for its owner’s tragic fall. The comics have done so more than once – most notably in the original Secret Wars #12, when an all-powerful Doctor Doom wiped the collective heroes off the map – and the MCU tapped into that vein with Tony Stark’s vision during Avengers: Age of Ultron. The implication in that moment was that Thanos was powerful enough to destroy the shield... a supposition that was borne out in Avengers: Endgame when the mad Titan’s blade sawed the top of the shield off.

Beyond that, however, the list of characters who could damage the shield grows thin. It blocked a direct blow from Thor’s hammer during the pair’s brief fight early in the original Avengers movie, and similarly withstood a full-bore attack from Tony’s Iron Man suit in Captain America: Civil War. The only earth-bound figure to significantly damage the shield is Black Panther, whose claws are also made from vibranium, and left marks on it during their tangle in Civil War.

What If…? finally answered the question of which hero could conceivably break it. Season 1, Episode 8, “What If… Ultron Won?” depicted a triumphant Ultron inhabiting the body of Vision and systemically destroying the Avengers. Cap’s death isn’t shown on-screen – Ultron saved that moment for Tony – but the sight of his shield shattered into pieces told the audience everything they need to know. In the process, the episode confirmed that Vision could destroy the shield.

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Vision Has The Power to Wreck Captain America's Shield

A close-up of Captain America's broken shield from What If as it lays on the ground

Vision’s immense powers rarely came into play during his tenure in the prime MCU. Wanda Maximoff had the raw power to fight against him – which suggests that Scarlet Witch might be able to break the shield too – but otherwise he kept his abilities strictly in check. It was in line with his moral code, which embraced life and sought to protect it in all circumstances. That manifested itself most obviously in Civil War, when he used the power of the Mind Stone to halt or rein in Rogers’ forces rather than cause them any direct harm. Furthermore, destroying the shield would serve no purpose, and regardless of Rogers’ fate, Vision would want to preserve it for use by some future hero.

Ultron had none of those principles, of course, and was more than happy to bring Vision’s full powers to bear on anyone standing in his way. The brief, heartbreaking shot of the shattered shield confirmed how readily the Vision could dispose of it if he wished, and answered the question about his comparative strength in the process. Ironically, the gesture – taking only a second or two of screen time – also reinforced one of the What If...? episode’s larger messages. Like Vision, Uatu hesitates to use his power when faced against Ultron. Heroes have to pick and choose when to unleash their abilities. Villains don’t, which always makes them tougher to beat than they should be.

What If...? Season 1 is available to stream on Disney+.