Robert Downey, Jr. has confirmed that he will have a cameo in The Incredible Hulk as Iron Man's Tony Stark. It will be small, but will help establish the convention of Marvel film characters appearing in other Marvel movies. Although he didn't want to ruin the surprise, Downey says that he will at least interact with General Ross, played by William Hurt in the film.
Also, there are rumors of guest appearances in Iron Man, but no one yet knows who or what they will be, though Hilary Swank and Samuel Jackson are rumored. However, as Iron Man gets closer, that will no doubt be a hard secret for the filmmakers to keep.
MTV Movies Blog: Robert Downey Jr Talks ‘Iron Man,’ ‘Hulk’ Cameos