The original screenplay was much darker. Apart from being a low-life, Hancock was supposed to be sexually frustrated because he couldn't have sex with a woman without killing her. The MPAA actually cleared a scene involving Hancock's explosive orgasm, but it was removed from the final cut because a test audience didn't find it funny. The tone was lightened considerably for a summer release aimed at a wide audience, but the MPAA gave the film an R twice before language and violence cuts resulted in a PG-13.
Will Smith is a native of Philadelphia, home of the Philadelphia Eagles. The eagle on the back of Hancock's uniform is a replica of the Eagles logo from 1948 to 1995.
The original title was "Tonight, He Comes." The script, which floated around in Hollywood for over a decade, was later retitled "John Hancock", then finally retitled "Hancock".
Will Smith is a huge fan of professional wrestling. He describes Hancock as Steve Austin, one of his favorite wrestlers, with super powers.
The movie was shown at a U.S. military base, in the Middle East for a week, before it opened in the U.S. The screening was free to all U.S. military personnel on base.