X2: X-Men United is the second part of the trilogy, following X-Men (2000) and preceding X-Men: The Last Stand (2006). It was directed by Bryan Singer, and starred an ensemble cast including Patrick Stewart, Hugh Jackman, Ian McKellen, Halle Berry, Rebecca Romijn, Famke Janssen, James Marsden, Anna Paquin, Brian Cox, Shawn Ashmore, Aaron Stanford, Kelly Hu and Alan Cumming.

The film is loosely based on the 1982 X-Men graphic novel God Loves, Man Kills. In the film, William Stryker is a high-ranking army colonel who leads an assault into Professor Xavier's school to build his own version of Xavier's mutant-tracking computer Cerebro in order to destroy every mutant on Earth. The X-Men are forced to ally with Magneto and Mystique to defeat Stryker. X2: X-Men United, which introduced Nightcrawler to filmgoers, surpassed the initial film at the box office, earning $215 million in North America compared to $157.3 million for X-Men, making the sequel one of the top ten movies of 2003.