Even the true form of Vrool is not known. His physical form is sometimes described as a red skinned devil with massive obsidian horns. Sometimes he is a dog-faced Daemon with long black antlers. To some he is dark skinned vampirc shadow, and in some descriptions, he’s a white winged asexual golden haired youth holding a spear.
Like his varied portrayal, the legends of Morpheus Vrool are vague and diverse. Some maintain he is a Daemon Prince, borne out of a failed experiment by the God Tzeentch to assassinate the Emperor in his slumber on the Golden Throne. Others say he is both the two-fold spawn and rival of Slaanesh, destined by prophecy to consume his own mother at the end of time and bring order to Chaos. Others still, assert he is no more than a favoured Prince of Chaos and not the Demigod of mythos. Whoever or whatever Morpheus Vrool is, his name has been invoked by a variety of ancient alien races and now the blood cults of Agrippa.
It is said that there is even a rare Eldar sect that believes Vrool is the nemesis of She who has no name and will rise to be the salvation of the Eldaran soul as interpreted by the ancient runes of Sethnor. For Humanity, in the spires of the urban hives, or the farthest most rural worlds, one form or another of the graven filth of the blood cults that worship him spread across Agrippa like a pandemic. Vrool invites the favour of all 4 Chaos powers and thus serves as a perfect vehicle for the conspirators among mankind. Officials from the Ordo Malleus who have spent their lives in pursuit of Vrool warn he may be the single largest threat to the Imperium of Man in the Agrippa Sector.
Since their arrival in the Agrippa sector the Twelvers have come to believe that Vrool is the Adversary, the Daemon responsible for the loss of the Twelfth company and their Time of Troubles. Whether this is founded in fact, or mere a convenient focussing of ancient enmities on a new enemy, the Twelvers it has placed them in direct opposition to Vrool's plans in the Agrippa Sector.