The Walt Disney Company acquired Marvel in 2009, meaning that Disney owns popular characters like Spider-Man, the Incredible Hulk and Captain America.
What does this mean for Universal Studios Orlando? Over there they have Marvel Super Hero Island in Islands of Adventure. It is themed to the comics of Marvel. Not any of the Disney productions. Just the comics since it was built before Disney bought Marvel. It has rides such as The Incredible Hulk Coaster and Adventures of the Amazing Spider-Man. You can also meet the comic versions of characters like Spider-Man, Captain America, and Cyclops.
Due to the contract, Universal has with Marvel from back in the 1990s, certain Marvel characters cannot appear on rides or in-person in Disney Parks on the east coast of the US. They can only be in Universal Studios Florida. This means, that all the Marvel characters can appear in Disneyland or the parks around the world, just not Disney World. More specifically, in regards to Disney World, they cannot belong to the large “families” such as the Avengers, X-Men, or Sinister Six.
What can appear in Disney world? Lesser-known characters like those in Big Hero Six can appear in person in Disney World. Also, Disney can still create rides about some characters such as Guardians of the Galaxy: Cosmic Rewind and they can sell the merchandise for their shows and movies in their park stores.
Who knows what the future holds for Marvel in theme parks, but Universal does not look like they are giving up their land any time soon.