Konrad Curze

"He would never be as charismatic as Lion El'Johnson, as articulate as Roboute Guilliman, as demagogic as Horns the Favoured... but he could be strong. He could shatter any enemy. He could be pragmatic. He could be terrifying.... He had never been human, but like all the primarchs there lurked in some deep corner of his luminous heart a flavour - a bitter taste - of humanity.
Konrad Curze sacrificed it. He wiped tears of insanity from snowy cheeks and cast his warmth to the wolves, and he did it in the Emperor's name. He lost everything.
He became what he had always been destined to; what the galaxy demanded he become; what the Emperor himself sanctioned, moulded, needed: He became a loyal monster" (from "Lord of Night" by S. Spurrier)