According to Tim Roth, Edward Norton re-wrote scenes every day. Norton and Liv Tyler also spent hours discussing their characters' lives (especially before the Hulk appeared).
Captain America: Civil War (2016) is the first reappearance of William Hurt as General Thaddeus Ross since this film, an eight-year absence for his character. The Russo brothers, directing that film, wanted to incorporate Ross, as they felt that character had been forgotten a bit since this film.
Paul Soles, who portrays "Stanley Lieber", the owner of the pizza shop, provided the voice for Bruce Banner/The Hulk in the Hulk (1966) animated series and later went on to provide the voice of Spider-Man/Peter Parker in Spider-Man (1967). The character's name is another tribute to Hulk co-creator Stan Lee. Stan Lee's birth name was Stanley Lieber.
Originally, Abomination was going to return as a supporting antagonist in Avengers: Age of Ultron (2015), but he was cut.
Michael Kenneth Williams: As a bystander in Harlem. Edward Norton wrote the part specifically for him, because he was a big fan of Williams' work on The Wire (2002).
Stan Lee: (at around 13 mins) the comic writer who co-created The Incredible Hulk in 1962 is the man who drinks the soft drink contaminated with Bruce Banner's blood.
Rickson Gracie: (at around 5 mins) appears as the Jiu-Jitsu instructor that is teaching Bruce Banner breathing exercises.
Paul Soles: As pizzeria owner Stanley Lieber. Soles voiced the Hulk in The Marvel Super Heroes (1966) and Hulk (1966). His character's name is a reference to the real name of Hulk co-creator Stan Lee.