This Character Pack was released as a free download during Games Workshop's second Skulls for the Skull Throne promotion on Steam.
From press release -
Rogal Dorn joins the Loyalists - a being of thunderous zeal and stone made manifest. To him there is no higher purpose to the ‘Legiones Astartes’ than the illumination of the Imperium’s ideals. His unyielding nature make Rogal Dorn both a master of defence in war, and an indomitable fighter on the attack.
Battling against the loyalists is the traitor Samus, a terrifying Daemon Prince of the Ruinstorm, whose ghostly whispers can destroy anyone in his path. As billions are slaughtered across countless worlds, the power of the Daemon waxes strong.
This character pack comes with new Custom Legion Data-slates and Encounter Data-slates.