Marvel has a Hulk... but what they don't have, apparently, is the full rights to do a Hulk movie.
While Marvel has used the Hulk in both Avengers film as well as the 2008 Incredible Hulk film they produced, Hulk actor Mark Ruffalo tells Collider that Universal Pictures' ownership of some rights is affecting any plans Marvel might have for another solo Hulk film.
"As far as a Hulk movie, a standalone Hulk movie, Marvel doesn’t really have the rights to that yet," Ruffalo reveals in the Collider interview. "That’s still Universal’s property, so there’s that issue. That’s a big impediment to moving forward with that. Now I don’t think that’s insurmountable, by the way, but I don’t know where it’s going from here for me."
What Ruffalo is seemingly referring to isn't the full movie rights, but rather the distribution rights to a standalone Hulk film.
Universal Pictures originally obtained the full movie rights to the Hulk back in 1992, eventually making the 2003 Hulk film directed by Ang Lee. In 2006, Marvel Studios announced announced it had re-acquired most of the rights -- barring distribution -- from Universal. Universal distributed Marvel Studios' 2008 Incredible Hulk film, and was an active participant in the production and promotion of the film.
After Disney acquired Marvel, it began a series of deals with Paramount to re-acquire distribution rights Marvel had previously sold to companies such as Paramount for Iron Man, Captain America and Thor. According to Ruffalo's statements, Marvel has not worked out a similiar deal with Universal Pictures for those rights for the Hulk.