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?
Sentence (from "Exo (band)"): 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.
Relevant evidence: No