Ever since Samuel Muther F’in Jackson appeared in the first Iron Man movie, speculation on the story for Avengers movie have run rampant. The one theory that continually appears is that the Avengers would be an adaptation of The Ultimates by Mark Millar and Bryan Hitch.
General Nick Fury of S.H.I.E.L.D. establishes a strike force of government-sponsored metahumans which includes Captain America; scientist couple Henry and Janet Pym (Giant-Man and the Wasp); Bruce Banner (the Hulk) and Tony Stark (Iron Man). Together they are based at the S.H.I.E.L.D facility, the Triskelion. When Banner injects himself with the super-soldier serum and goes on a bloody rampage as the Hulk, he is eventually stopped by the other metahumans with the aid of Thor. The team then join forces with the mutants Quicksilver and Scarlet Witch and agents Hawkeye and Black Widow against the alien shape-shifters the Chitauri, who are defeated.
Except for the concept art that appeared during our San Diego Comic Con coverage, we really haven’t seen or heard what role the Hulk will play in the movie. However, the second half of the Wikipedia entry regarding an alien invasion appears to lend support to the Chitauri invasion – or at the very least a Kree-Skrull War plot – thanks to new images captured in Cleveland during Chris Evans’ scenes being shot this week.
While adaptation could significantly change the look of Kree/Skrull alien crafts, the motion tracking suit the actor in the last image is wearing means something not human will appear in the movie.