Genestealer Magus

And then I say, "Let there be bitches and hoes!" and they delivered.

And deliver they did.

A Genestealer Magus, sometimes simply called a Magus, is a high ranking person in a Genestealer Cult, the 'right-claw humanoid' of a Genestealer Patriarch and one of the ones that looks the most 'human'. A Genestealer Magus acts as the 'chief psyker' of a Cult, and he uses his psychic influence to manipulate and cast away the authorities of the Imperium.

Overview

The Magus plays a vital role in infiltrating a civilized society. Due to his (or her. There's even a female Magus model now!) intelligence, charisma, appearance, and understanding of the society being infiltrated, he is well suited to his role as mouthpiece of the clan to the outer society. The Magus is a special mutation which appears in a clan if a psychically-active species, such as humanity, is infiltrated. As a Genestealer Hybrid of the 4th generation, he appears nearly human, although is invariably bald and heavy boned (which the Magus can just bullshit as "being born that way"). He is highly intelligent and possesses formidable psychic ability. His "normal" appearance allows him to operate as the public spokesman for the clan or cult, which is disguised as a legitimate religious, political, or social movement — a role which the purestrain Genestealer Patriarch cannot take.

Magi are always born from at least one parent who is a Psyker, and this, combined with its xenos DNA, makes the creature a highly potent psychic being. He can use his psychic abilities to coerce or enslave others to his cause. Should a Patriarch or Magus dominate a region completely, the psychic shadow that gathers around him will grow darker and thicker until it begins to coalesce. This ever-shrinking miasma hardens into a many-limbed form known as a Genestealer Familiar that will faithfully serve its Magus.

The Magus is second in importance to the Patriarch; under these two individuals there is little hierarchy or leadership. Therefore, both the Magus and the Patriarch are the primary targets of Imperial Assassins. Killing both of these individuals leaves the Genestealer Cult leaderless and in disarray, allowing a military force to follow up and purge the mass of fanatics.

Magi are rare in correlation with how rare Psykers are in the parent population, so a Genestealer Cult is drastically more dangerous on a planet with more Psykers around.