Happy birthday, Michael Jackson

The King of Pop passed away four years ago. But fans still send him birthday greetings.

Michael Jackson had a career fit for a superstar, full of astronomic highs and shocking lows. The singer passed away on June 25, 2009, from cardiac arrest, leaving behind a legacy as the king of pop.  Robert Deutsch, USA TODAY

Today would have been Michael Jackson's 55th birthday. Though the King of Pop died four years ago at the age of 50, Twitter was full of birthday greetings and retrospectives of the late singer.

The Jackson 5, made up of Jackson and his older brothers (from left, Tito, Marlon, Michael, Jackie and Jermaine), perform on the 'Sonny and Cher Comedy Hour' television program in Los Angeles. The group was a fixture on variety shows and even had their own cartoon series.  AP

Also, producer Timbaland hinted at a new project that could include Jackson's vocals. In a teaser initially posted on YouTube's Revolt TV channel, Timbaland talked about being approached by Epic Records executive L.A. Reid about a project that "would be like two kings working together." Timbaland never mentions Jackson's name, but the singer's image appears throughout the clip, which has appeared in several third-party versions since the original was removed from YouTube.

Here's a Spotify playlist featuring Jackson's biggest hits.