The Nephilim were a minor but malevolent xenos species first encountered on the human-settled world of Melchior by the Blood Angels and the Luna Wolves Space Marine Legions during the Great Crusade in the late 30th Millennium. They fed on the mental emanations of adoration and religious ecstasy and subjugated Melchior's native human population -- and the populations of many other worlds in the region colonised by Mankind -- in order to satisfy this constant psychic hunger.
The Nephilim towered over even Horus, and were twice as tall as an Astartes. They moved slowly, like beasts swimming through water, but could move much faster when in combat. Their native language used hypersonic frequencies and flashes of bio-luminescence, making it impossible to translate for humans. To speak Low Gothic, they utilised a cybernetic implant to generate a vibrating field that created sounds audible to humans; this implant could also be used as a Sonic Weapon. Their hands had three stubby fingers. Their social hierarchy was defined by the different colours of their bloated, oblate bodies: blue represented the "rank and file", green the "squad sergeants", and grey the Nephilim "commanders".
The Nephilim fed on psychic adulation. They arrived on new worlds and preached a message of spiritual salvation and eventual heavenly reward. Through either psychic manipulation or their alien sheer charisma, the Nephilim converted human populations to their religion. They fashioned masks of their own flesh for their devotees, which were fused to their faces and psychically bonded them together. In turn, the faithful built praise-chapels and copper towers to their alien saviours. The Nephilim consumed lives through psychic means, leaving their faithful as desiccated husks. By the time the Luna Wolves and Blood Angels fought the Nephilim on Melchior, the xenos had stripped multiple worlds in the region of all human life.
Horus Heresy Edit
Years later, in the early days of the Horus Heresy, the Warmaster Horus tricked his fellow Primarch Sanguinius into taking his Blood Angels Legion to the Signus Cluster, claiming that the Nephilim had not been exterminated, but had returned to enslave the human population again. Horus also deceived Sanguinius into believing that the Nephilim, with their powers of mental manipulation, possessed a device that could cure the Blood Angels' secret genetic affliction.
- Fear to Tread (Novel) by James Swallow