The first rule of being the Hulk is, you don’t talk about being the Hulk. At least for Mark Ruffalo, that is, who has revealed he is not allowed to discuss the idea of doing a Hulk solo movie—if you ask me, he’s already broken the rule by admitting that, but we’ll let him off.
You’d think the MCU can do whatever it wants, given the mammoth success the franchise has achieved over the last 15 years. So why has there never been a Hulk solo movie? Looking back at the Marvel movies in order, he’s always been part of a team, and looking ahead to upcoming Marvel movies, there’s still no sign of Hulk going it alone.
The answer is simple: Marvel doesn’t actually fully own the rights to the Marvel character (sounds stupid, I know) and the studio is not allowed to profit off any Hulk-specific superhero movie. On the matter, Ruffalo told ComicBook.com: “I’ve been asked not to comment on it, that specifically.”
Sounds serious, right? Well, Ruffalo—being the blabbermouth he is—proceeded to then comment on the situation in more detail. When asked if a Hulk movie will ever happen, he said: “Not that I know of… Hopefully one day though they’ll work it out. I think it could be really cool and I’ve been putting a lot into what it could be to be cool, but I don’t know yet.”
To put it simply, Universal owns the rights to the Hulk, and the MCU is only allowed to put him in a film or Marvel series which centers on other heroes (e.g. Thor Ragnarok, the Avengers movies, or the She-Hulk series). Until those legal wrinkles are worked out, we will never see this version of the Hulk doing his own thing in the MCU.
There’s a good chance we will never see it, in fact. Despite a decent level of demand for a Hulk movie, there is no indication that Kevin Feige and co. are working towards a solution. The plans for Marvel’s Phase 5 and Phase 6 include no mention of Hulk, though we can assume he will be in Avengers 5 and Avengers Secret Wars.