Back in Phase 1, The Incredible Hulk star Edward Norton was replaced in the Marvel Cinematic Universe with actor Mark Ruffalo, who recently opened up about the awkward situation. Released in 2008, The Incredible Hulk introduced the MCU's Hulk with Norton, following the success of MCU starter Iron Man that same year. A number of behind-the-scenes issues led to Norton exiting the role after the movie's release, with Ruffalo officially announced as the new Hulk actor in 2010 for The Avengers. Now that some characters from The Incredible Hulk have returned to the MCU, Ruffalo has opened up about the awkward replacement.
https://screenrant.com/mark-ruffalo-edward-norton-hulk-replacement/