EXO

EXO is a 12-member boy band under SM Entertainment. The members are split into two subgroups of 6, called EXO-K and EXO-M to promote in Korean and Mandarin, respectively. After a series of teasers and prologue songs, EXO debuted with "MAMA" in April.

Pre-debut
After SM announced the formation of the new boy band, a series of 23 teasers were released over three months, from December 2011 to March 2012. Each one showcases the members' talents and provides snippets of EXO's songs.

"What is Love" and "History"
The music videos for EXO's first prologue song, "What is Love," was released on January 29, 2012. The Korean version features the voices of D.O. and Baekhyun, while the Mandarin version features Luhan and Chen. The videos for both versions are compilations of clips from the teasers to display the 12 members.

On March 8, 2012, SM released the music videos of "History."

Showcase and Debut
EXO performed their debut showcase in Korea on March 31, 2012 and in China on April 1, 2012. They revealed their for the first time the teaser and performance for their debut song, "MAMA."

"MAMA" was released on April 7, 2012. The video displays the members with various super powers and connects each member of EXO-K with one in EXO-M.

"What Is Love"
2012, prologue single

"History"
2012, prologue single

MAMA
2012, debut mini-album
 * 1) MAMA (debut single)
 * 2) What Is Love
 * 3) History
 * 4) Angel
 * 5) Two Moons (ft. Key of SHINee)
 * 6) Machine

Citation
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http://sumandu.wordpress.com/kpop-profiles/boy-groups/exo-m-profile/