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 [fn 1] ), 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 year 2014 and 2015. They have been named "the biggest boyband in the world" by media outlets, saying that "EXO are at the forefront of pop domination, with knifepoint choreography seamlessly gelled to songs crafted by some of the world’s most gifted writers and producers, honed by their myriad of personalities and talents." 
In May 2014, Kris filed a lawsuit against S.M. Entertainment to be removed from the group. Luhan followed suit in October 2014. In April 2015, Tao suspended his activities and subsequently followed suit in August 2015. Following their departures, Exo carried on with nine members. In July 2016, it was announced that the lawsuit between Luhan, Kris, and S.M. Entertainment had been settled: the two idols will maintain their contract with SM until 2022, S.M. Entertainment will contract out their work outside of Korea and Japan—i.e. to their current Chinese agencies—and they will "share related revenues with S.M. Entertainment".
Source : wikipedia