Ahriman - 13th Black Crusade: In his quest for the forbidden knowledge of the Aeldari's Black Library, Ahriman is known to have breached the Webway twice, both times during the 13th Black Crusade in 999.M41. In the first instance, Ahriman was able to gain access to the Webway using knowledge extracted from the captured Inquisitor Bronislaw Czevak. Czevak had been the only Human ever invited by the Asuryani to be a "guest" of the hidden craftworld that is the Black Library -- in reality he had been used by the Aeldari as bait and a foil for Ahriman.Ahriman subsequently entered the Webway through a long-forgotten portal that was discovered by his minions on the world of Etiamnum III, a planet bequeathed to the care of the Imperium by the Asuryani of Craftworld Altansar before that craftworld had been lost in the Eye of Terror millennia before. This intrusion was considered a major setback by the Asuryani Farseers who had failed to foresee it, and none other than Eldrad Ulthran himself, the greatest of the Farseers, had to be summoned from Ulthwé to lead the Asuryani defence against the breach.Ahriman was eventually repulsed, and the Webway gate he had used to gain entry was sealed, never to be opened again. The secretive Order Psykana, which consists exclusively of Blood Ravens Librarians, was also called to help defeat the Traitors but arrived too late, and they subsequently took over the protection of the Imperial reclusium that housed the Webway portal.A short time later, Ahriman's prodigious psychic and occult powers allowed him to foresee a rip into the Webway inadvertently caused by the Blood Ravens Librarian Rhamah near the planet Lorn V during the Chapter's operations on that Ice World. Accompanied by his warband of Thousand Sons sorcerers he called the Prodigal Sons, Ahriman approached the planet under stealth, and used his sorcery, the aid of Daemons, and the transdimensional rip caused by Rhamah to find a Webway portal to Arcadia, the Aeldari Planet of Law.The world was the exclusive domain of Harlequins, and contained a masterfully concealed Aeldari settlement including an extensive Librarium, a repository of Aeldari history and technology. Ahriman utilised a book that was considered a myth, The Tome of Karebennian, which he had taken from the Harlequin Solitaire of the same name, to attempt to find one of the Arcadian Webway portals leading to the Black Library. He additionally sought to steal an artefact known as the Sword of Lanthrilaq, a potent weapon used by the Aeldari aeons ago against the C'tan, during the War in Heaven, which was held by Arcadia's Great Harlequin.Ahriman and the Prodigal Sons had also captured the Daemonifuge and former Sister of Battle Ephrael Stern, who he intended to use against his rivals following his conquest of the Black Library. Despite summoning a Leviathan, a giant flying Warp beast similar in size and shape to a manta ray, and inflicting horrendous casualties on both sides of the conflict, Ahriman was ejected from the Webway with his goal unattained.Following the end of the 13th Black Crusade, Ahriman's star is once again on the rise with the Thousand Sons' Daemon Primarch Magnus the Red, mostly due to the great chaos caused by his battles against the Aeldari within the Webway, the prowess he displayed in capturing Inquisitor Czevak, and the extraordinary knowledge and ability required to even come close to entering the fabled Black Library.It is rumoured that if Ahriman ever gained full entry into the Black Library, he could use the sum total of the information contained within it to become a new and powerful Chaos God within the Warp.