Iron Man's Hulkbuster armor returns in Anthony and Joe Russo's Avengers: Infinity War, but that doesn't mean Tony Stark is wearing the mega-suit. The Hulkbuster armor is an exo-frame armor set worn by Iron Man in order to go toe-to-toe with and potentially defeat fellow Avenger the Hulk should the green giant ever pose a threat to either the team or innocent bystanders. The armor set first appeared in Iron Man Vol.1 #304 back in 1994, but it has since become an inspiration for other Avenger-buster armor sets, such as the Thorbuster.
The last time audiences saw the Hulkbuster armor on-screen was in Joss Whedon's Avengers: Age of Ultron. In the film, Tony (Robert Downey Jr.) donned the modular add-on set in order to stop Hulk from terrorizing a nearby city after he was temporarily affected by Scarlet Witch's (Elizabeth Olsen) powers. Since Hulk disappeared after that incident and only reappeared in Taika Waititi's Thor: Ragnarok, Tony hasn't had any reason to use the armor, but the first trailer for Avengers: Infinity War is teasing the Hulkbuster armor's return - but what if Tony isn't the one piloting it?
In the Infinity War teaser trailer, Bruce Banner (Mark Ruffalo) is seen standing next to the Hulkbuster's right forearm attachment (above), which is curious considering the armor's sole purpose is meant to defeat him. Well, at least "the other guy." Then, at a later point in the teaser, the Hulkbuster armor is seen in action outside what appears to be Wakanda. What's interesting is that Hulk is also later seen fighting alongside Wakanda's army (whereas Iron Man is not). What if Hulk is actually the one donning the Hulkbuster armor in Avengers: Infinity War, perhaps after snapping out of Hulk and being unable to transform back? We've definitely learned after Spider-Man: Homecoming that Iron Man armor doesn't necessarily mean Tony Stark, and although it sounds far-fetched, there is a precedent.
Bruce Banner wore Iron Man's armor into battle in Avengers Assemble #6 (above), released in August 2012. After charging into battle, Iron Man's armor exploded, thus transforming Banner into the Hulk. As it turns out, Tony had the genius idea to send Hulk first as a Trojan horse. And here's the interesting part: in that particular comic issue, the Avengers joined forces with the Guardians of the Galaxy (a lineup that heavily resembles the one in the MCU) to defend Earth against an invasion from the Mad Titan Thanos (sound familiar?). Perhaps something similar will transpire in Avengers: Infinity War.
Hulk is nigh-indestructible (he's arguably the most powerful superhero in the Marvel Universe), but that doesn't mean he's not vulnerable against an opposing force such as Thanos, especially if the Mad Titan is brandishing a completed (or near-complete) Infinity Gauntlet. The Hulkbuster armor could give him somewhat of an edge against the supervillain, or maybe the Russos will adopt that particular comic issue onto the big screen.
We'll just have to wait and see what happens when Avengers: Infinity War hits theaters next summer, but such a trick is certainly in the realm of plausibility, especially with Tony Stark involved.