Boogieman

The Boogieman (also known as Sun Moon Stars and also described as Flatulence by Jamie Hewlett) is one of the antagonists of the Gorillaz. Murdoc mentioned in his live chat with fans that the Boogieman was the essence of everything bad in the world in one person, though Murdoc's opinion of him may very well have been biased as the two were mortal enemies at the time.

Background
The Boogieman is a rejected "5th Horseman" of The Four Horsemen of the Apocalypse and his real name is Flatulence, because of the foul smell he always brings with him.

Gorillaz Phase 3: 2010-2012
Boogieman made his appearance in Phase 3. His first appearance is in 2-D's Plastic Beach Ident where he is seen gassing 2-D. He is first fully seen in the "Stylo" music video in which he engulfed a highway patrol officer in a black smog before vanishing. In the "On Melancholy Hill" music video, he kidnapped a crying manatee atop of Melancholy Hill for no explained purpose. Cyborg Noodle fired two solid slugs at the Boogieman, which resulted in him pulling the manatee down with him off of the hill into the sea. He is next seen in the storyboard video for Rhinestone Eyes, where he appears to Murdoc on Plastic Beach, displays a memory of Murdoc and his agreement, and attacks Plastic Beach, summoning several planes similar to those that had attacked Noodle in the On Melancholy Hill video.

Murdoc has stated in a blog on the Gorillaz website that he'd made some deals with the Boogieman (which, Murdoc said, was actually a demon) to ensure a career at the top of the music charts and to get rid of some unwanted people. In turn, Murdoc would give access to "various souls of innocent kids and stuff". Murdoc, however, made sure he wasn't around when the Boogieman would come by to collect his payment. And now he'd returned to take revenge on Murdoc (it is possible that gassing 2D was his last job for Murdoc). Murdoc also stated that he was shocked to see him in the Stylo music video footage, as he hadn't noticed him before.

When the Boogieman invaded Plastic Beach during the events of Rhinestone Eyes, Murdoc had The Imposter Murdoc take his place so the wrong soul would be collected, settling the debt between the two.

In the "DoYaThing" music video, he appears in the living room while reading a newspaper of completely normal form before glaring at 2-D.

Gorillaz Phase 5: 2018-2019
In the FreeMurdoc campaign Murdoc said that he had no idea what was going with the Boogieman as he unfriended him after he kept sending yoga pics.

In The Now Now Q&A on June 29th, 2018, two different answers were given when was asked what happened to the Boogieman. One was that he became a star in the Boogie Nights  and the other was that he is now working as personal chef for the Gorillaz, as of Murdoc's arrest.

Trivia

 * The Boogieman is the first Gorillaz antagonist to ever appear in the band's music videos.
 * Despite the fact the the Boogieman is treated as an enemy, in the On Melancholy Hill and Stylo music videos and the Rhinestone Eyes storyboard, he is seen in 2-D's Phase 3 ident gassing him. This could explain why 2-D says that Murdoc 'had' him gassed, but would imply that the Boogieman and Murdoc were working together; it may be possible that this was the case, but it wouldn't explain why he is seen as an antagonist. It could also be that Murdoc saved 2-D from the Boogieman after he was gassed and never told him.
 * The fact that the Boogieman is actually a demon explains how he could disappear with the Police Officer in the Stylo music video.
 * His name "Sun Moon Stars" is referenced in the song Sweepstakes.
 * According to Jamie Hewlett, The Boogieman is actually a rejected "5th Horsemen" of The Four Horsemen of the Apocalypse and his real name is Flatulence, because of the foul smell he always brings with him. This explains why he appeared with The Horsemen in the storyboarded "Rhinestone Eyes" video.
 * The character in the Sweepstakes Picture with the white mask is called Evangelist. It's a human or creature who is related to the Boogieman, however it is portrayed as good. Jamie Hewlett opened a contest on the Gorillaz website to see what the Evangelist looks like under its mask and robes.The winning entrant designed the Evangelist as a woman, soaking wet with a fish bowl upon her head, rain boots on her feet, and squids hanging off her arms.
 * It has been rumored on different websites that Boogieman may be Hannibal Niccals, Murdoc's older half-brother. However, it is unknown and probably unlikely that this is true, as Hannibal was put into jail for "stealing hubcaps," according to Murdoc in Rise of the Ogre.
 * In the "DoYaThing" video, the Boogieman appears at 2-D's house reading a newspaper. When 2-D arrives to the living room, the Boogieman turns his face to 2-D. It is not explained, as lots of other things about the video, why is the Boogieman at 2-D's house, and specially, why didn't he try to attack 2-D, Noodle, or even Murdoc (who also appears in the video), and why 2-D doesn't seem to be surprised when he sees Sun Moon Stars.
 * Boogieman's appearance could be a reference to Dream's Helm, a character from Neil Gaiman's Sandman series.
 * Noodle (or even Cyborg Noodle) was going to shoot the Boogieman.