- Actor Allusion:
- Dianna Agron once again used to date the quarterback and is now one of the misfits.
- John says about Agron's character "she's not just another girl". Agron featured in the music video for The Killers' "Just Another Girl".
- Henri tells Number Four "you have no idea what you are capable of". This is a nod to Timothy Olyphant saying a similar line Die Hard 4.0.
- Actor-Inspired Element: Number Six is Australian because Teresa Palmer wanted to speak in her natural voice.
- Actor-Shared Background: Dianna Agron loves photography about as much as character Sarah, having her own collection of digital and film cameras.
- Cast the Expert: Alex Pettyfer was already trained in stunt work and combat from Stormbreaker, making him an apt fit for Number Four.
- Dawson Casting: Played straight as 24-year-old Dianna Agron, 22-year-old Jake Abel and 20-year-old Alex Pettyfer play high school students. 24-year-old Teresa Palmer as 16-year-old Six, too. However, it's averted with Callan McAuliffe who was 15 at the time of filming, and Greg Townley who was 14: their characters' ages.
- Deleted Role: Karen Allen filmed some scenes as Sam's mother, but they were cut from the film.
- Dyeing for Your Art:
- Alex Pettyfer dyed his blond hair brown for the beginning of the film. Jake Abel dyed his blonde hair brown for the duration of the film. Callan McAuliffe had his hair dyed darker for the film, but claims to have lost track of its original color because he's dyed it other colors for roles before.
- Teresa Palmer went through three months of sword training, wire work and weight training to prepare.
- Fake American: Alex Pettyfer is British.
- Follow the Leader: A very pretty boy moves into a small town and starts a relationship with a girl, except he has superpowers, which complicates things. And his mouthy, socially ostracized friend is called Sam, who believes in ancient astronauts. Number Four even ends the movie narrating that Earth is his home now,
and though they are worlds apart, there's more to them than meets the eyeso he has to protect it.
- Stillborn Franchise: Not the novels, but the film series that was intended to be released alongside the novels was shelved indefinitely due to lukewarm reception and mediocre box office profits.
- Romance on the Set: Alex Pettyfer and Dianna Agron became Dialex for a bit.
- What Could Have Been: Sharlto Copley was cast as Henri, but dropped out due to scheduling conflicts, and was replaced with Timothy Olyphant.
Trivia / I Am Number Four