At the beginning of the Age of Chaos, many Gargant tribes either sought to flee from the invaders or join Sigmar's alliance to resist them. Others however were eventually corrupted mind and body by Chaos, descending into savagery and with their forms twisted in bestial fashion. Chaos Gargant tribes trample the lands and slaughter everything they can, caring nothing for each other and banding together only to increase their destructive powers.
Chaos Gargants were a faction introduced in the Grand Alliance: Chaos in the first edition. During the 2nd edition rulebook this faction was entirely subsumed by the Monsters of Chaos faction