Chaos Raptors
Raptors are Chaos Space Marine Assault Marines. Or, at least, they were at first. Then Games Workshop decided that they needed something original about them and made them separate from the Legions, turning them into mercenary warbands, or "cults" who don't worship the big four, instead worshipping the "Raptor God". And now they're Chaos Assault Marines again. Games Workshop sure is indecisive.
And despite what people might tell you, the Night Lords are NOT the "Raptor Legion". Though they are creators of Raptor squads and dictinctive Raptor armour with clawed feets and large engine intakes, so Night Lord bands often have laghe ammount of Raptors in their ranks. This is more like Word Bearers and Possessed or Iron Warriors and Obliterators - they are distinctive brand of the legion, yet not really abundant, and not having real political power, being treated by "normal" marines like little more than a beasts.
Speaking about Raptor armour, it seems GW retconned old awesome one with predatory helmet, brutal-looking jump-pack and bird-like fanged legs for the lame heresy-era armour with two beer kegs on the back and stupid little blades on the feet. Not like it is the first time GW replaces cool model design with derpy one.
See also Warp Talons, for their mutant daemonic 6th Edition elite version.