The June 2008 Marvel Studios title The Avengers.
However, that doesn't mean the project hasn't gotten referenced in subsequent projects, with The Incredible Hulk's improvised post-credits scene (which, unlike every other MCU title, actually played just before the credits), which featured an appearance by Robert Downey Jr. as Tony Stark.
It's a scene depicting a meeting between Hurt's Ross and Downey Jr's Tony Stark in a dimly-lit tavern, one which ends with Stark asking Ross what his feelings would be if he told the general that he was putting some kind of team together. Obviously a tease for the then-forthcoming Avengers movie, it's a scene that cemented The Incredible Hulk as taking place in a larger universe, but it provided obvious continuity issues once subsequent movies came to fruition. The most pressing of these issues being why Stark would be sent to recruit people for The Avengers after the events of Iron Man 2 (which take place before The Incredible Hulk) made it clear S.H.I.E.L.D. saw Stark as too much of a liability to be involved with The Avengers.
An attempt to rectify this issue and other continuity quibbles manifested in the 2011 short film The Consultant, one of the entries in Marvel's short-lived series of Marvel One-Shot short films. This short saw Agent Phil Coulson (Clark Gregg) and Agent Jasper Sitwell (Maximiliano Hernandez) engaging in a series of conversations that provided greater context to this Tony Stark/Thunderbolt Ross conversation. Specifically, it was revealed a volatile personality like Stark being sent on a recruitment mission was the whole point. A retcon was established that Ross wanted Emil Blonsky's Abomination (the villain of The Incredible Hulk) to the Avengers rather than remain in prison.
getting around continuity issues found in one of Marvel Studios' earliest movies. Its primary legacy is serving as another example of how Marvel's been grappling with incorporating The Incredible Hulk into the larger Marvel Cinematic Universe.
