Question: What is this South Korean-Chinese boy group formed by S.M. Entertainment in 2011 initially with several members and broke up a year later that released the song "Mama" in 2012?

Context paragraphs:
Exo (band): Exo (Korean: 엑소 ; stylized as EXO) is a South Korean-Chinese boy group based in Seoul.  Formed by S.M. Entertainment in 2011, the group debuted in 2012 with twelve members separated into two subgroups, Exo-K (Suho, Baekhyun, Chanyeol, D.O., Kai, and Sehun) and Exo-M (Xiumin, Lay, Chen and former members Kris, Luhan and Tao ), performing music in Korean and Mandarin respectively.  Exo's first album "XOXO" (2013), which contained the breakthrough hit "Growl", was a critical and commercial success, winning both Disk Daesang at the 28th Golden Disk Awards and Album of the Year at the 15th Mnet Asian Music Awards.  It sold over one million copies, making Exo the best-selling Korean artist in twelve years.  Subsequent albums and EPs continued with strong sales, and Exo were ranked the most influential celebrity by "Forbes" Korea Power Celebrity for the years 2014 and 2015.  They have been named "the biggest boyband in the world" by media outlets.

Ex'Act: Ex'Act is the third studio album by South Korean-Chinese boy band EXO.  It was released by S.M. Entertainment in Korean and Chinese versions on June 9, 2016.  The album was re-released under the title Lotto on August 18, 2016.  "Ex'Act" is the third consecutive studio album by EXO to have sold over 1 million copies, and their fourth album to have won the Mnet Asian Music Award for Album of the Year.

Mama (Exo song): "Mama" is a song by South Korean-Chinese boy bands Exo-K and Exo-M.  It served as their debut single and title track from their debut record "Mama" (2012).  Available in both Korean and Mandarin, the song was digitally released on April 8, 2012, by S.M. Entertainment.

Exo videography: EXO is a South Korean-Chinese boy band produced by S.M. Entertainment.  Separated into subgroups EXO-K and EXO-M, respectively performing music in Korean and Mandarin, the band debuted on April 8, 2012 with the single, "Mama".  Prior to debut, various members of the band have modeled in music videos performed by senior S.M. Entertainment artists.

Mama (EP): Mama is the debut studio EP by South Korean-Chinese boy band Exo-K and Exo-M, produced and released by S.M. Entertainment on April 9, 2012 in two language editions – Exo-K's Korean version and Exo-M's Mandarin version.

Overdose (EP): Overdose is the second EP by South Korean-Chinese boy bands EXO-K and EXO-M.  It was released by S.M. Entertainment and distributed by KT Music on May 7, 2014 in Korean and Chinese version.  It is preceded by their special EP album "Miracles in December" that was released in December 2013.  This is the final release that includes members Kris and Luhan before they left the group and filed lawsuits against S.M. Entertainment requesting contract termination.

Miracles in December: Miracles in December (Korean: 12월의 기적 ; ) is the overall second EP by South Korean-Chinese boy band Exo.  It was released by S.M. Entertainment on December 9, 2013.  Presented as a special winter album, "Miracles in December" is a follow-up to the group's first studio album "XOXO", which was released in June 2013.  Like all of the group's music, the EP has Korean and Chinese versions.  The EP is also the group's second release as well as first EP to be promoted extensively being as a combined group.  Its singles were "Miracles in December" and "Christmas Day".

XOXO (album): XOXO is the first studio album by South Korean-Chinese boy band Exo, released on June 3, 2013 by S.M. Entertainment.  The album is a follow-up to the group's debut EP, "Mama" (2012).  Like all of the group's music, the album was released in two versions – a Korean "Kiss" edition and a Chinese "Hug" edition.

The War (album): The War is the fourth studio album by South Korean-Chinese boy band EXO.  It was released digitally on July 18, 2017 and physically on July 19, 2017 by S.M. Entertainment under Genie Music's distribution.  The album includes a total of nine tracks including the lead single "Ko Ko Bop".  "The War" received the highest number of pre-orders at that time for a K-pop album, at more than 800,000 physical copies.  24 days after being released, it became EXO's fourth consecutive studio album to have sold over a million copies.  The album was re-released under the title The War:" "The Power of Music on September 5, 2017.

Exo discography: The discography of the South Korean-Chinese boy band Exo consists of four studio albums, five extended plays, and twenty one singles. Exo was formed by the Korean entertainment company S.M. Entertainment in 2011, and formerly consisted of twelve members separated into two sub-groups, Exo-K and Exo-M, releasing the same music simultaneously in both Korean and Mandarin in South Korea and China, respectively.  The group's first release, the extended play "Mama", was released in April 2012.  The album topped Korean music charts on its release.

Supporting paragraphs: Mama (Exo song) Exo (band)
Answer: Exo