M'Shen

M'Shen is the famous Callidus assassin whom successfully assassinated Night Haunter, the traitorous Primarch of the Night Lords Legion. Within all of Imperial history, she is definitely known to have been the only assassin who has successfully assassinated a Primarch.

Background
Following the destruction of Nostramo, Konrad Curze chose the world of Tsagualsa (referred as 'The Carrion World'), located on the outer reaches of the Eastern Fringe, as his base of operations. The Night Haunter had a grotesque palace built, made entirely from still living bodies. From here, he launched a massive campaign of genocide against the Imperium that made the Night Lords Legion's previous atrocities pale in comparison, before or since. M'Shen located Night Haunter on Tsaguala and managed to infiltrate his palace, stealing into his throne room. Despite Night Haunter's formidable powers of foresight which obviously forewarned him of the assassination attempt, he took no extra precautions to defend himself. It is believed she was allowed to infiltrate his palace, as M'Shen encountered no guards between herself and Night Haunter's throne room. When confronted by the Callidus assassin he allowed himself to be killed to vindicate his decisions to destroy his homeworld of Nostramo and to rebel against the Emperor. Before his death, M'Shen's vid-log records Night Haunter's enigmatic last words, "Your presence does not surprise me, Assassin. I have known of you ever since your craft entered the Eastern Fringes. Why did I not have you killed? Because your mission and the act you are about to commit proves the truth of all I have ever said or done. I merely punished those who had wronged, just as your false Emperor now seeks to punish me. Death is nothing compared to vindication." The vid-log then shows M'Shen leaping forward, although the kill was never confirmed, as the video feed cuts out right before they fight. After the assassination, M'Shen cut off the Night Haunter's head to take to her masters as proof of her kill and many of the Primarch's personal items and trinkets (including the Corona Nox). Enroute back to her ship she was confronted by Talos, declaring to him that she would forever after be remembered by historians as the 'Godslayer'. The assassin and the Night Lord Astartes briefly fought one another, but M'Shen managed to flee and escape.