U2 Mullen's father suggested that he place a notice on the Mount Temple bulletin board, U2 was founded on 25 September 1976 in Mullen's kitchen in Artane. McCormick and Martin soon left, and the group settled on the name "Feedback" because it was one of the few technical terms they knew. During the recording of the album
Pop in 1996, Mullen suffered from severe back problems. Recording was delayed due to surgery. When he left the hospital, he arrived back in the studio to find the rest of the band experimenting more than ever with electronic drum machines, something driven largely by the Edge's interest in
dance and
hip-hop music, and, given his weakness after the operation, he relented, allowing The Edge to continue using drum machines, which contributed heavily to the album's electronic feel. In order to recuperate from surgery, Mullen did not perform during U2's concert residency
U2:UV Achtung Baby Live at Sphere, which ran for 40 shows from September 2023 to March 2024 at
Sphere in the Las Vegas Valley. Dutch drummer
Bram van den Berg from the band
Krezip filled in for him. It was the first time that Mullen missed a U2 show since 1978, when he broke his foot in a motorcycle accident.
Other projects Mullen has worked on many musical projects outside of U2 in his career, including collaborations with
Maria McKee. Mullen contributed to U2 producer
Daniel Lanois's 1989 album
Acadie. In 1990, Mullen co-wrote and arranged an official
Ireland national team song "
Put 'Em Under Pressure" for the
FIFA World Cup. He and Clayton collaborated with
Mike Mills and
Michael Stipe from
R.E.M. to form the one-performance group Automatic Baby, solely for the purpose of performing "
One" for
MTV's 1993 inauguration ball for US President
Bill Clinton; the group's name refers to the titles of both latest bands' albums at the time,
Achtung Baby and
Automatic for the People. For
Nanci Griffith's 1994 album
Flyer, he and Clayton performed in the rhythm section on several songs, while Mullen also mixed three songs. Mullen played drums on many of the songs on
Emmylou Harris' 1995 album
Wrecking Ball. Mullen and Clayton contributed to
the soundtrack of the 1996 film
Mission: Impossible, which included reworking the "
Theme from Mission: Impossible", whose time signature was changed from the original time signature to an easier and more danceable
time signature. The song reached number 8 on the U.S.
Billboard Hot 100, and was nominated for the
Grammy Award for Best Pop Instrumental Performance in 1997. Mullen performed on
Underworld's song "
Boy, Boy, Boy" from their 2007 album,
Oblivion with Bells. In 2017, he appeared on
Alice Cooper's album
Paranormal. Mullen has played synthesiser or keyboards on several songs, including "United Colours" from Passengers' 1995 album
Original Soundtracks 1, an album that Mullen has always disliked. ==Musical style and techniques==