Magus

"'Well well, well. Look what we have here. I had a feeling you had guts, detective. I just didn't realize how badly you wanted them spilt.'"The Magus is the public face of a Genestealer Cult on Hive World Purgatory. He acts as the "new mayor's spokesman," and attempts to foil Detective Bruce Norring's investigation.

Official Canon
A Magus is a special genestealer hybrid born from psychic parents. The Magus is a potent psyker himself, and will use his charisma to bring he cult together, as well as divert suspicion away from the cult. Being among the most human-looking hybrids, the Magus will be out in charge of any front organizations used by the cult. He will also act as an enforcer of the Patriarch's will.

TTS Canon
The unnamed Magus intercepts Bruce on his way to the mayor's residence, and introduces himself as the new mayor's spokesman. Bruce was immediately suspicious of this "uncanny excuse for a man." The Magus attempted to have Bruce silenced before he could reveal the existence of the cult, but when the latter snuck into the cult's lair, he was instead to be made into a gene host. The Magus and the rest of the cult, however, were all killed when Inquisitor Adrielle Quist suddenly emerged from the Warp.

Personality
The unnamed Magus is shown to be scheming and cunning as well as extremely charming up and to a point. It is heavily implied he had the hives previous mayor killed or infected and held sufficient sway following this to intimidate almost everyone into silence. He projected a sense of confident security and approached Bruce Norring in an attempt to set him up for an ambush that Brue was able to avoid through using the backdoor. Which while speaks of his ability to manipulate and indeed intimidate, his oily charms were not able to sway Bruce, likely due in part of his tendency to imply subtle hints to the truth in an attempt to avoid giving a direct answer.

Within the safety of the Gene stealer sanctuary he drops this polite and oily charisma, and confronts questions more directly. He indeed seems to become increasingly unhinged after realising Bruce managed to connect with the Hive Mind clearly revealing his fanatical devotion to his god, talking with almost perverse pleasure as he observed Bruce almost being infected.

Quotes

 * "Seize his mind! Infect him! TYRANNICUS IA F'TAGHN!!"