Question: Which singer is also a musician, Gwen Stefani or Charlie Simpson?
Context: Gwen Renée Stefani ( ; born October 3, 1969) is an American singer, songwriter, fashion designer, actress, and television personality.  She is a co-founder and the lead vocalist of the band No Doubt that experienced major success after their breakthrough studio album "Tragic Kingdom" (1995) along with various successful singles, including "Just a Girl", "Don't Speak", "Hey Baby", and "It's My Life".  During the band's hiatus, Stefani embarked on a solo pop career in 2004 by releasing her debut studio album "Love.  Angel.  Music.  Baby. " Inspired by pop music from the 1980s, the album was met with both critical and commercial success.  It spawned three commercially successful singles: "What You Waiting For? ", "Rich Girl", and "Hollaback Girl", the latter reached number one on the "Billboard" Hot 100 while also becoming the first US download to sell one million copies.  In 2006 Stefani released her second studio album "The Sweet Escape".  The album produced two successful singles: "Wind It Up" and the album's title track "The Sweet Escape".  Her third solo album "This Is What the Truth Feels Like" was released in March 2016 and became her first solo number-one album on the "Billboard" 200. Charles Robert "Charlie" Simpson (born 7 June 1985) is an English singer, songwriter and musician.  He is the youngest member of multi-BRIT Award-winning band Busted, and is the lead vocalist, guitarist in post-hardcore band Fightstar.  AllMusic has noted that Simpson is "perhaps the only pop star to make the convincing transition from fresh-faced boy bander to authentic hard rock frontman".  Simpson is a multi-instrumentalist, playing guitar, keyboard, piano and drums. "Hollaback Girl" is a song recorded by American singer Gwen Stefani for her debut solo studio album, "Love.  Angel.  Music.  Baby. " (2004).  As part of Stefani's vision of creating "a silly dance record", "Hollaback Girl" is a hip hop song that draws influence from 1980s hip hop and dance music.  The song was written by Stefani, Pharrell Williams and Chad Hugo, supposedly as a response to Courtney Love's statement that Stefani was a "cheerleader" in an interview with "Seventeen" magazine.  The song was released as the album's third single on March 15, 2005, and was one of the year's most popular songs, peaking inside the top 10 on the majority of the charts it entered.  It reached number one in Australia and the United States, where it became the first digital download to sell one million copies. "The Sweet Escape" is a song by American singer and songwriter Gwen Stefani from her second studio album of the same name (2006).  It was written by Stefani, Akon, and Giorgio Tuinfort.  Akon, who is also a featured artist, developed the song's beat before collaborating with Stefani.  He designed it based on her previous work with No Doubt, and Stefani later commented that it put her "on the yellow brick road to the No Doubt record I might do".  "The Sweet Escape" is an apology for a fight between two lovers and describes a dream of a pleasant life for them.  As the album's title track, its title was chosen to help market Stefani's music and fashion lines. "Sunday Morning" is a song recorded by American rock band No Doubt.  It was released as the sixth single from their third studio album "Tragic Kingdom" (1995).  The single was made available as a CD single, cassette single, and VHS single on May 27, 1997 through Interscope.  Lyrically, the song is about Gwen Stefani's relationship with Tony Kanal, and their breakup that followed.  The track was written by band members Kanal, Gwen Stefani, and Eric Stefani, while production was handled by Matthew Wilder. "What You Waiting For?"  is a song by American singer Gwen Stefani from her debut solo studio album, "Love.  Angel.  Music.  Baby. " (2004).  Written by Stefani and Linda Perry, the song is the album's opening track and was released as Stefani's debut solo single.  "What You Waiting For?"  details Stefani's lack of inspiration, fear of producing the album, as well as her reaction to pressures exerted by her record label.  It is primarily an electropop song and introduces Stefani's four back-up dancers, the Harajuku Girls, who had a major input into the album's production. "Shine" is a song recorded by American singer Gwen Stefani, featuring collaborative vocals by American entertainer Pharrell Williams.  Originally intended for Stefani's band No Doubt, it was written and produced by Williams, with songwriting contributions from Stefani.  It is a reggae pop and ska song that is featured in the 2014 animated film "Paddington."  The lyrics revolve around the lead character Paddington Bear's journey to London and his identity crisis.  Stefani initially disagreed with Williams' choice to use direct references to Paddington in the lyrics, but praised this decision after watching the film with her children.  She reported that her involvement with the recording was inspired by her then-husband Gavin Rossdale and her children's connection to England. American singer and songwriter Gwen Stefani has recorded material for three studio albums and one extended play (EP), and has been featured on songs on other artists' respective albums.  After releasing five studio albums with ska punk group No Doubt, in 2004 Stefani began work as a solo artist, developing her pop debut "Love.  Angel.  Music.  Baby. " in the same year.  It produced several top ten singles worldwide, including "What You Waiting For? ", "Rich Girl", and "Hollaback Girl", the latter of which was the first single to sell over a million digital copies in the United States.  The record contained work from a variety of producers and songwriters, including Linda Perry, Nellee Hooper, André 3000, and No Doubt bandmate Tony Kanal. " Cool", "Luxurious", and "Crash" were also released as the singles.  In 2005, Stefani released an extended play "Love.  Angel.  Music.  Baby.  (The Remixes)" and included the Richard X remix of "Cool", which topped the United States Dance Club Songs in November 2005.  Hip hop musician André 3000 made two appearances on the album, including on "Long Way to Go", and his alter ego "Johnny Vulture" on "Bubble Pop Electric". This Is What the Truth Feels Like is the third studio album recorded by American singer and songwriter Gwen Stefani.  It was released on March 18, 2016 by Interscope Records.  Initially, the album was scheduled to be released in December 2014 with Stefani working with a handful of high-profile producers, and Benny Blanco serving as executive producer.  However, after the underperformance of her 2014 singles and the writer's block Stefani suffered, she did not feel comfortable curating an album and scrapped the whole record in favor of starting again.  The album's release was scheduled after Stefani hinted at it on her Twitter account. "Spark the Fire" is a song recorded by American singer and songwriter Gwen Stefani.  The song was released on December 1, 2014.  It was originally intended to be featured on Stefani's third studio album "This Is What the Truth Feels Like," but it was scrapped in favor of new material.  Stefani wrote "Spark the Fire" in collaboration with the song's producer Pharrell Williams.  It is a dance-pop and hip hop track that incorporates funk.  Along with the previous single, "Baby Don't Lie", the track was marketed as Stefani's musical comeback as a solo artist.
Answer: Charles Robert "Charlie" Simpson