Jack's last name came from a character we've seen in La Femme Nikita (1997) (Peter Bauer, #1.06). The famous split screen we see in 24 was used on La Femme Nikita #1.03 and Jack's motto "whatever it takes" is said by Michael and Madeleine in the first season of La Femme Nikita.
After working on 24, Freddie Prinze Jr said that working with Kiefer Sutherland almost made him quit the acting business.
Paul Blackthorne, who plays season 3 main villain, Saunders, originally auditioned for the role of Amador, another one of the season 3 villains. After failing the audition, his agent negotiated with the producers and managed to get the role of Saunders.
Kim Bauer is abducted a total of six times
Jayne Atkinson originally auditioned for the role of The President's wife, Martha Logan, in Season 5. Jean Smart was eventually cast as Mrs. Logan, and Atkinson was later cast in the role of CTU executive Karen Hayes. In a subsequent interview, Atkinson said that her audition for the role of Martha Logan had gone well, but that Jean Smart was perfect for the part. In addition, she felt a stronger connection to her role as Karen Hayes.
Seasons 2, 3 and 6 are the only seasons where CTU hasn't employed any moles or double agents.
In the Day 5 episode 4:00 p.m.-5:00 p.m. Audrey identifies herself to the secretary as Jane Espenson. Jane Espenson is a writer who had previously worked with David Fury (one of 24's producers), on several Joss Whedon shows.
At the power plant before Palmer's breakfast speech, Jack runs into old friend and Palmer staffer, Jessica Abrams. In conversation, she refers to mutual old friend Tracy Zigler, who had erroneously reported that Jack and Teri had divorced. Both characters are named after members of the production crew; Jessica Abrams is the script coordinator, and Tracy Zigler is the script supervisor.
Glenn Morshower portrays Agent Aaron Pierce throughout the series. Kiefer Sutherland's father, Donald Sutherland's "star-maker" role was in MASH (1970), as Capt. Benjamin Franklin (Hawkeye) Pierce.
Harris Yulin, who plays the recurring character of NSA director Roger Stanton in Season 2, is not credited at all in the opening or ending credits. All recurring and guest stars have to share their credits on screen with one or two other actors, but Yulin wanted to appear alone on them. Because this was not possible, he decided not to be credited at all.
In the fifth episode of the fourth season, Debbie's cell phone rang with a valid California phone number on the caller ID. Many fans noticed this and called the number, Some callers heard a voice mail message telling them that they called the 24 prop phone and to leave a message. Others spoke with various people, including Production Designer Joseph A. Hodges and stars Kim Raver (Audrey Raines) and Carlos Bernard (Tony Almeida). Hodges later stated in an interview that director Jon Cassar came up with the idea for the "Fan Phone" because the two of them often got bored scouting new shooting locations and wanted a chance to interact with the audience. Hodges indicated they received around 80,000 calls on the line in the first week. There is also a valid California cell phone number on S03E03, Chase's cell number appears in Jack's cell.
Roughly 25 hours of footage are edited into one episode of the show.
When the series was continued after the success of the first season, there were plans to abandon the real-time format, and resume with more conventional episode formats (i.e. cutting out time periods and making episodes more stand-alone). However, several series prominents, including main star Kiefer Sutherland, successfully pleaded to keep the real-time format.
The Season 6 plotline involving hostiles taking over CTU headquarters and Jack's nephew eluding them by crawling through air ducts almost exactly parallels a plotline from 24: The Game (2006), except that in the game it was Jack's daughter Kim eluding the terrorists.
Nina Myers' fake passport shows Sarah Clarke's own married name (Sarah Berkeley), but not her birthday, which is in 1972 (the passport shows 05.05.1975).
Over the course of the series, many guest actors previously starred or would go on starring on Stargate SG-1 (1997) or one of its spin-offs. Among them: Michael Shanks, Robert Carlyle, Paul McGillion, Louis Ferreira, Lou Diamond Phillips, Carlo Rota, Reiko Aylesworth and William Devane.
Michael Shanks was even filming 24 and Stargate: Continuum (2008) concurrently. Due to his commitment to 24, he is absent from a portion of Stargate: Continuum (2008).
William Devane played the President of the United States in both Stargate SG-1 (1997) and 24: Live Another Day (2014).
According to Gregory Itzin, while the cast and crew of 24 were on a tour of Washington D.C., they learned that Supreme Court Justice Clarence Thomas is a huge fan of the show.
Jack Bauer has a Bachelor's Degree in English Literature from UCLA and a Master's Degree in Criminology and Law from UC Berkeley. Kim Bauer has an Associate's Degree in Computer Programming from Santa Monica College. President Palmer has a Bachelor's Degree in Political Economy from Georgetown University, and a Juris Doctorate from the University of Maryland School of Law. Tony Almeida has a Bachelor's Degree in Engineering and Computer Science from San Diego State University and a Master's Degree in Computer Science from Stanford University. Michelle Dessler has a Bachelor's Degree in Computer Science from UC Davis. Sherry Palmer has a Bachelor's Degree in Sociology from Georgetown University.
Each even numbered season of the series (2, 4, 6 and 8) deal with a nuclear threat to the country.
After the show had become wildly popular, a tag line in reference to the main character circulated among viewers; "How many lives does 'Jack' have?" (Stemming from the extreme circumstances that Jack faced each day.) In the film "Speed", Joe Morton's character Lt. McMahon asked the same question of the main character "Jack" Traven.
Alan Milliken of Season 3 shares the same last name as 24's Transportation Coordinator, Dennis Milliken.
Jack was only an official CTU employee for 3 of the 8 seasons; in season one as the CTU Director, in season 2 his credentials are reinstated after being "inactive" for 18 months and in Season 3 as Director of Field Ops. During each of the other seasons, he was "contracted" as a freelance and given temporary clearance; in season 4 he asks Erin Driscoll to reinstate him on a provisional basis. (With the exception of season 7, as CTU had been disbanded)
Both Dennis Haysbert (David Palmer) and Penny Johnson Jerald (Sherry Palmer) had supporting roles in the political thriller Absolute Power (1997) starring Clint Eastwood.
With eight seasons 24 became the longest running show with themes involving espionage counter-terrorism.