The Bound are parodies of humanity, created in vats by the Fae and loosed into the Realms to oppose Realmwalkers. 
The Bound are hideous parodies of humanity that attack on sight. Who would create such crude mockeries? And why?
"Whilst the Fae Realms are home to a variety of strange and bewildering creatures, few are as disturbing to behold as these hideous parodies of humanity. When they first appeared, they attacked on sight - overwhelming the towns and hamlets. Diverse in their form, they are unified by their aggression and by the strange ligatures that crisscross their skin. The Redcrosse Knights knew them of old as ‘Bound’, whilst the Hermetics of the Academy theorized that they were magickal creations. But who so hates mankind to make such mockeries? And why?" - Elizabeth Cochran Seaman
"The Bound, a faction created by the adversarial Fae as a "mimicry of humanity" to combat the player RealmWalkers. The Bound come in many forms, including minion creatures, long-range attackers, magic users, tank-like creatures, and a bruiser seen in the trailer with a wheel for a head" - Neal Thompson