The late great entertainer supposedly came up with the moniker himself, asking MTV to call himself with such nickname.
As instantly as Michael Jackson began to be referred to as "The King of Pop", so did people quickly assumed that the artist got that moniker by his sheer talent and artistry, as he was indeed one of the greatest pop superstars ever. However, MTV drops the bomb that the late great entertainer actually came up with the moniker himself and demanded to be called as such.
This revelation is included in the book "I Want My MTV: The Uncensored Story of the Music Video Revolution" by Rob Tannenbaum and Craig Marks. According to them, Jackson sent a memo to MTV back in 1991 requesting that VJs refer to him as The King of Pop. He apparently wanted every network that would be airing his then newly-released "Black and White" video to call him by that nickname.
The book went as far as to reveal that MTV bosses, who owed Jackson a debt of gratitude, required VJs to use the moniker at least twice a week. Some hosts even had to re-tape entire shows just so they could work in the moniker, just in case Jackson asked for clips.
According to Larry Stressel, an Epic Records executive during that time, Jackson had talked to him about wanting to have his own nickname, much like Elvis Presley is dubbed "The King" or Bruce Springsteen is called "The Boss", even hiring personal publicist Bob Jones to issue a press statement declaring Jackson as "The King of Pop". Despite some negative feedback at the time, the label obeyed his request, as no one could contest the fact that Jackson is indeed the greatest pop superstar of all-time.