2011: Formation and early beginnings

In January 2011, producer Lee Soo-man of S.M. Entertainment announced his plans to debut a new boy band in March or April 2011.Temporarily namedM1, the group appeared to have consisted of only seven members when a photo of them in a dance studio leaked online.In May 2011, Lee spoke about the group in a Hallyu business seminar held in Stanford University . In the presentation, he explained his strategy of separating the group into two subgroups, M1 and M2, and have them promote the same music in both Korea and China, performing the songs in both Korean and Mandarin .Lee planned to launch the group in May 2011, but their debut was delayed and news concerning the group did not surface until October 2011, when Lee briefly discussed about the group's concept plans in an interview withThe Chosun Ilbo.

In December 2011, the group finalized their name to EXO, with the names EXO-K for the Korea subgroup and EXO-M for the China subgroup. Their name was taken from exoplanet ,a term referring to planets outside of the Solar System . The twelve members were introduced individually through twenty-three different teaser trailers released from December 2011 to February 2012. Kai , Lu Han , Tao , and Chen , the first four members introduced, debuted their first public performance at the SBS 'sGayo Daejunevent on December 29, 2011.

2012–present: Debut andMAMA

EXO-K and EXO-M's prologue single " What Is Love " was released on January 30, 2012, through iTunes and various online retailers from China and South Korea,where the single peaked at number eighty-eight on South Korea's Gaon Single Chart . On March 9, the group released their second prologue single " History ,"which was written and produced by Thomas Troelsen and Remee . The single peaked at number sixty-eight on the Gaon Single Chart and number six on China's Sina Music Chart.

A concert showcase for the group was held in Seoul's Olympic Stadium on March 31, one hundred days after EXO debuted their first trailer on December 21, 2011.Approximately 3,000 fans from 8,000 applicants were selected to attend the showcase.A second showcase was held in the Great Hall of the University of International Business and Economics in Beijing , China on April 1.

EXO-K and EXO-M released their debut single " Mama " on April 8,followed by an EP ,Mama, on April 9. On April 8, EXO-K made their debut performance on South Korea's music programThe Music Trend, while EXO-M performed at China's12th Yinyue Fengyun Bang Awardsthat same day.One day after release, "Mama" reached number one on various Chinese online retailers and music charts.EXO-M's album peaked at number two on China's Sina Album Chart and number five on South Korea's Gaon Album Chart , while EXO-K's album peaked at number one on the Gaon Album Chartand debuted at number eight on the Billboard World Albums Chart .EXO-M's "Mama" music video peaked at number one on Chinese streaming websites, and EXO-K's version reached to number seven on YouTube's Global Chart.

EXO-K

• Suho – Leader
• Kai
• Sehun
• D.O.
• Baekhyun
• Chanyeol

EXO-M

• Kris – Leader
• Lu Han
• Tao
• Chen
• Lay
• Xiumin

EPs

• 2012:MAMA

1. EXO to officially debut on April 9th with “MAMA”
2. ["http://www.allkpop.com/2012/04/exo-k-and-exo-m-releases-mama" "EXO's "Mama" released"]. allkpop.com. April 7, 2012. "http://www.allkpop.com/2012/04/exo-k-and-exo-m-releases-mama". Retrieved April 7, 2012. 
3. "SM Entertainment to debut new male group in March/April 2011". Allkpop. 2011-01-29. http://www.allkpop.com/2011/01/sm-entertainment-to-debut-new-male-group-in-marchapril-2011. Retrieved 2012-04-09. 
4. "Practice photo of SM Entertainment’s upcoming boy group “M1″ leaked!". Allkpop. 2011-03-22. http://www.allkpop.com/2011/03/practice-photo-of-sm-entertainments-upcoming-boy-group-m1-leaked. Retrieved 2012-04-09. 
5. "SM's Lee Soo-man announces new boy band" (in Korean). Nate.com. 2011-05-09. http://news.nate.com/view/20110509n18306. Retrieved 2012-04-15. 
6. "Lee Soo Man on his system of management, upcoming groups M1 & M2, and his dreams". Allkpop. 2011-10-17. http://www.allkpop.com/2011/10/lee-soo-man-on-his-system-of-management-upcoming-groups-m1-m2-and-his-dreams. Retrieved 2012-04-09. 
7. "SM introduces new boy group member, KAI". Allkpop. 2011-12-23. http://www.allkpop.com/2011/12/sm-introduces-new-boy-group-member-kai. Retrieved 2012-04-09. 
8. "EXO releases teaser #23!". Allkpop. 2012-03-01. http://www.allkpop.com/2012/03/exo-releases-teaser-23. Retrieved 2012-02-13. 
9. "EXO makes their debut at SBS ‘Gayo Daejun’". Allkpop. 2011-12-29. http://www.allkpop.com/2011/12/exo-makes-their-debut-at-sbs-gayo-daejun. Retrieved 2012-04-09. 
10. http://news.nate.com/view/20120127n03950?mid=e0101
11. EXO to Release Prologue Single "What Is Love" on January 30
12. The Prologue Single II 'History' will be released on the 9th
13. "Sina Music Charts 2012-03-12" (in Chinese). Sina.com. http://rank.music.sina.com.cn/20120312/sina-xg-day.html. Retrieved 2012-04-11. 
14. EXO (2012-04-06) (in Korean and Mandarin Chinese). EXO_SHOWCASE HD Full version Part 3_ENG. S.M. Entertainment via YouTube. http://www.youtube.com/watch?v=ri4Z4DcicsE. Retrieved 2012-04-11. 
15. "EXO debuts in front of 3000 fans". Korea.net. 2012-04-01. http://m.korea.net/english/NewsFocus/e-newsWorld/view?pageIndex=1&articleId=378. Retrieved 2012-04-13. 
16. "S.M.'s new group EXO first press conference in China" (in Chinese). Sohu.com. 2012-04-01. http://ent.sina.com.cn/s/j/2012-04-01/21493596302.shtml. Retrieved 2012-04-13. 
17. "The First Mini Album Title Song ‘MAMA’ of EXO-K and EXO-M will be Released Worldwide on the 8th at 00:00!". http://www.facebook.com/#!/notes/smtown/the-first-mini-album-title-song-MAMA-of-exo-k-and-exo-m-will-be-released-worldwi/364494690260038. Retrieved 11 April 2012. 
18. ["http://www.facebook.com/notes/smtown/exo-k-and-exo-m-will-make-their-debut-on-april-8th-both-in-korea-and-china-/361970087179165" "EXO to debut on April 8, 2012"]. facebook.com/smtown. April 3, 2012. "http://www.facebook.com/notes/smtown/exo-k-and-exo-m-will-make-their-debut-on-april-8th-both-in-korea-and-china-/361970087179165". Retrieved April 3, 2012. 
19. " "EXO-K debuts on Inkigayo with "MAMA"". allkpop.com. April 8, 2012. http://www.allkpop.com/2012/04/exo-k-make-history-with-their-debut-of-MAMA-on-inkigayo". Retrieved April 8, 2012. 
20. "韩团EXO-M《MAMA》雄踞中国音乐榜榜首 [Korean group EXO-M's single "Mama" reaches number one in China]" (in Chinese). Sohu.com. 2012-04-10. http://ent.sina.com.cn/y/2012-04-10/16043601595.shtml. Retrieved 2012-04-13. 
21. "[Gaon Album]" (in Korean). Gaon. http://gaonchart.co.kr/main/section/search/chart_list.gaon?Search_str=EXO-K. Retrieved 2012-04-21. 
22. "World Albums". Billboard.com. http://www.billboard.com/charts/world-albums#/charts/world-albums. Retrieved 2012-04-21. 
23. "EXO-K’s Music Video Comes In Seventh on Youtube Chart". Mnet. 2012-04-09. http://global.mnet.com/news/newsdetail.m?searchNewsVO.news_id=201204091703_5307. Retrieved 2012-04-13.