Avengers: Infinity War - 8 Compelling Theories About The Hulk
2. ... And He's A Villain (At First)
We already know from the Infinity War footage that the Hulkbuster is back, and while it might be tempting to suggest Tony Stark simply brings it out to try and deal with the bigger members of The Black Order, it is a very specifically built suit, and Stark isn't the type to use a square peg to fit a circular hole. If the Hulkbuster is in use, it's to bust Hulk, and that suggests he's going to fight his old friends.
So why would that happen? It could be simply an issue of him losing control completely, of course.
But, what if Thor leaving Hulk on Sakaar is a bigger disaster for the defenders of Earth than the implications of him being grumpy? What if it leaves a hugely valuable - and mostly invincible - weapon in the hands of Thanos as he travels across the universe on his quest for the Infinity Stones?
Putting together the hints that Hulk is angrier and is part of a key, intriguing arc throughout the Infinity Gauntlet storyline, there's an irresistible possibility that he will be recruited by Thanos (perhaps with a promise of him being "cured" by the Reality Stone?) and simply unleashed on the Avengers as a distraction while Thanos goes about the business of conquest.