
Mark Lee is a Korean-Canadian kpop idol. He debuted in 2016 as a member of NCT (Neo Culture Technology), a 25-member group that splits into sub-units, which are smaller groups so that each member can sing more than 0.2 seconds in a song. He’s in the most sub-units of all the members, AFAIK.
real answer tho, there r like hundreds (not that all of them r popular or well known) It’s kinda like how in America or wherever u r theres a lot of singers and artists in general. Instead of having these regular solo artists that we have, there’s a big group/band culture in Korea
Mark was a very central to the group, and arguably the most talented and iconic member that defined their sound. He was in multiple sub-units (aka being in multiple kpop groups at the same time) which led to him being extremely busy and overworked. He left all the groups entirely and basically quit being an idol, wanting to focus on a new chapter in his life.