Question: Which Metallica co-founder wrote the power ballad "Mama Said"?

full_context: Document 1: Kirk Hammett: Kirk Lee Hammett (born November 18, 1962) is an American musician who has been lead guitarist and a contributing songwriter for the heavy metal band Metallica since 1983. Before joining Metallica he formed and named the band Exodus. In 2003, Hammett was ranked 11th on "Rolling Stone"<nowiki>'</nowiki>s list of The 100 Greatest Guitarists of All Time. In 2009, Hammett was ranked number 15 in Joel McIver's book "The 100 Greatest Metal Guitarists".
Document 2: Hero of the Day: "Hero of the Day" is a power ballad by American heavy metal band Metallica from their 1996 album "Load". The song was first recorded on December 13, 1995, and was the first song on "Load" to be recorded. The song was also Metallica's second single release from the album. A promotional video for the track was also filmed. It became their second consecutive number-one hit on the US "Billboard" Hot Mainstream Rock Tracks chart. It is one of the few Metallica songs written primarily in a major key.
Document 3: Jimmy Page: James Patrick Page, {'1': ", '2': ", '3': ", '4': "} (born 9 January 1944) is an English musician, songwriter, and record producer who achieved international success as the guitarist and founder of the rock band Led Zeppelin.
Document 4: Load (album): Load is the sixth studio album by the American heavy metal band Metallica, released on June 4, 1996 by Elektra Records in the United States and by Vertigo Records internationally. The album showed more of a hard rock side of Metallica than the band's typical thrash metal style, which alienated much of the band's fanbase. It also featured influences from genres such as Southern rock, blues rock, country rock and alternative rock. Drummer Lars Ulrich said about "Load"'s more exploratory nature, "This album and what we're doing with it – that, to me, is what Metallica are all about: exploring different things. The minute you stop exploring, then just sit down and fucking die."
Document 5: The Unforgiven (song): "The Unforgiven" is a power ballad by American metal band Metallica. It was released as the second single from their eponymous fifth album "Metallica" (also known as "The Black Album"). Though one of the slower tracks on the album, its chord progression is distinctly one of the heavier. The song deals with the theme of the struggle of the individual against the efforts of those who would subjugate him.
Document 6: Jason Newsted: Jason Curtis Newsted (born March 4, 1963) is an American metal musician, known for being the third recording bass guitarist with the band Metallica from October 1986 until his departure in January 2001, as well as being a part of Voivod and Flotsam and Jetsam. After leaving Metallica he continued with his project Echobrain, played with Ozzy Osbourne and joined heavy metal band Voivod. Newsted uses the pseudonym Jasonic, which serves as both his alias in Voivod and the name of his music publishing company. He is also the founder of the Chophouse Records studio and label based in California. From 2012 to 2014 he played in his self-titled band Newsted, for which he provided lead vocals as well as bass. Newsted lives in Alamo, California.
Document 7: List of Metallica concert tours: Metallica is an American heavy metal band, founded in 1981 by drummer Lars Ulrich and rhythm guitarist James Hetfield. Aside from Ulrich, the original lineup for some of the 1982 concerts included James Hetfield (rhythm guitar and lead vocals), Dave Mustaine (lead guitar and backing vocals) and Ron McGovney (bass guitar). Cliff Burton replaced McGovney in 1982 and played with the band until his death in 1986. After his death, bassists Jason Newsted (1986–2001), and Robert Trujillo (since 2003) were recruited in the band. While the lead guitarist role was taken by Kirk Hammett (since 1983) after Dave Mustaine got fired from the band.
Document 8: Enter Sandman: "Enter Sandman" is a song by American heavy metal band Metallica. It was released as the first single from their eponymous fifth album, "Metallica" in 1991. The music was written by Kirk Hammett, James Hetfield and Lars Ulrich. Vocalist and rhythm guitarist Hetfield wrote the lyrics, which deal with the concept of a child's nightmares.
Document 9: List of songs recorded by Metallica: Metallica is an American heavy metal band formed in Los Angeles, California in 1981. The band released its debut album "Kill 'Em All" in 1983, which credited songwriting between frontman James Hetfield, drummer Lars Ulrich and guitarist Dave Mustaine, who had left before the album was recorded (bassist Cliff Burton was credited for the bass solo "(Anesthesia) – Pulling Teeth"). On the 1984 follow-up "Ride the Lightning", Burton received more songwriting credits and Mustaine's replacement Kirk Hammett was also co-credited on four songs. "Master of Puppets", released in 1986, was the last album to feature Burton, who died in a bus accident later that year.
Document 10: Metallica: Metallica is an American heavy metal band based in San Rafael, California. The band was formed in 1981 in Los Angeles when vocalist/guitarist James Hetfield responded to an advertisement posted by drummer Lars Ulrich in a local newspaper. Metallica's current lineup comprises founding members Hetfield and Ulrich, longtime lead guitarist Kirk Hammett, and bassist Robert Trujillo. Guitarist Dave Mustaine (who went on to form Megadeth) and bassists Ron McGovney, Cliff Burton, and Jason Newsted are also former members of the band.
Document 11: Metallica discography: The following is the discography of Metallica, a Los Angeles-based metal band formed in 1981 by James Hetfield (lead vocals, rhythm guitar) and Lars Ulrich (drums). After several bassist and lead guitarist changes, the band settled on Cliff Burton and Kirk Hammett, respectively. Metallica started playing locally, releasing their first widely circulated demo, "No Life 'til Leather", in 1982. The demo caught the attention of Johny Zazula, who signed Metallica to Megaforce Records. The band released "Kill 'Em All" in 1983, and the following year they released "Ride the Lightning". After "Ride the Lightning" was released, Metallica left Megaforce and signed to Elektra Records. In March 1986, the band released its third studio album, "Master of Puppets", which was Metallica's first album to be certified gold by the Recording Industry Association of America (RIAA). While promoting the album, Burton was killed in a bus accident. Jason Newsted was hired as a replacement. The band's first release to feature the new member was "," and then followed by "...And Justice for All" in August 1988, which peaked at number six on the "Billboard" 200.
Document 12: James Hetfield: James Alan Hetfield (born August 3, 1963) is an American musician, singer, and songwriter known for being the co-founder, lead vocalist, rhythm guitarist, and main songwriter for the American heavy metal band Metallica. Hetfield is mainly known for his intricate rhythm playing, but occasionally performs lead guitar duties and solos, both live and in the studio. Hetfield co-founded Metallica in October 1981 after answering a classified advertisement by drummer Lars Ulrich in the Los Angeles newspaper "The Recycler". Metallica has won nine Grammy Awards and released ten studio albums, three live albums, four extended plays and 24 singles.
Document 13: Mama Said (Metallica song): "Mama Said" is a power ballad by American heavy metal band Metallica from their sixth album "Load", with music and lyrics by James Hetfield (music credited to Hetfield/Ulrich). The lyrics represent a man or boy who is learning to find his own way in life away from his mother. The song is directly written about Hetfield's difficult relationship with his mother, who died of cancer when he was 16 years old.
Document 14: Lars Ulrich: Lars Ulrich {'1': ", '2': ", '3': 'R', '4': "} ( ; ] ; born December 26, 1963) is a Danish musician, songwriter, actor, and record producer. He is best known as the drummer and co-founder of the American heavy metal band Metallica. The son of tennis player Torben Ulrich and grandson of tennis player Einer Ulrich, he also played tennis in his youth and moved to Los Angeles at age 16 to train professionally. However, rather than playing tennis, Ulrich began playing the drums. After publishing an advertisement in "The Recycler", Ulrich met vocalist/guitarist James Hetfield and formed Metallica.
Document 15: List of songs performed live by Metallica: Metallica is an American heavy metal band from Los Angeles, California. The band was founded in 1981 by drummer Lars Ulrich and vocalist and rhythm guitarist James Hetfield, alongside lead guitarist Dave Mustaine and bassist Ron McGovney. Mustaine and McGovney were later replaced by Kirk Hammett and Cliff Burton, respectively. Burton died in 1986 and was replaced by Jason Newsted, who remained in the band until 2001, before Robert Trujillo joined. Since its first live concert on March 14, 1982, Metallica has played 2,012 official shows. As of their show on September 16, 2017, the band has performed 164 songs and medleys live.
ground_truth: James Hetfield