Kharn the Betrayer is a champion of Khorne.
Kharn had been the World Eaters' equerry prior to Angron's discovery by the Emperor. When all other captains failed to convince Angron to take command of the legion (and were brutally murdered), only Kharn succeeded. Kharn had befriended marines outside his legion during the Great Crusade, including Imperial Fists first captain Sigismund, but at the outbreak of the Heresy, he had already committed himself to Khorne.
After the Heresy, Kharn was single-handedly responsible for the breakup of the World Eaters legion when, during a battle with the Emperor's Children, he forced his fellow legionaires to fight by destroying their shelters. That is how he earned his epithet.
Kharn was booked to appear for the Slaaneshmas special, but turned down the offer and grumbled on the phone. His slot was taken by Sly Marbo. He is acknowledged as part of the unofficial "quartet" of Chaos Champions, comprised of Ahriman, Typhus, and Lucius.