Beyond the various Chaos factions dedicated specifically to one of the various Chaos gods, there's also the Beasts of Chaos who serve those foul beings. As Games Workshop keeps going through the various factions in Age of Sigmar and seeing how they're changing, they've come to this faction. Have yourselves a look.
From the article:
The self-proclaimed inheritors of the Mortal Realms are swarming out of the wilderness in a rage-fueled stampede. For the past few weeks, we’ve been talking about how the various factions play in the new edition of Warhammer Age of Sigmar. As the realm-shaking release of the Dominion launch box approaches, it’s high time the slavering Beasts of Chaos get their due.