SPOILER: In the opening credits, a blueprint of the sonic cannon at Culver University can be seen bearing the title "Stark Industries," indicating that it was Tony Stark (of Iron Man (2008)) who built the cannons for General Ross to use against the Hulk. Stark himself appears in the film's closing scene.
The opening credits sequence is a flashback showing how Bruce Banner became the Hulk and details his subsequent run from Ross, interspersed with military documentation archiving his progress.