Lukas Alexander was initially sent to Kronus to track down and capture Farseer Taldeer after her actions on Lorn V (Shown in Winter Assault). His forces landed in an abandoned city, and found traces of ancient relics scattered across the planet, including a "Hellstorm Cannon", a piece of weaponry from a Horus Heresy Era Imperator Titan. The city was renamed "Victory Bay", and techpriests began excavating the massive Hellstorm cannon. The Imperium then gave Lukas Alexander the title of "Governor-Militant" of Kronus, and tasked him with conquering the planet for the Imperium.
Alexander formed the 1st Kronus Regiment, which he named "The Liberators", since he believed his soldiers were fighting to free the humans who were on the planet. Unfortunately, his goals put him at odds with a Blood Ravens force who are on Kronus trying to uncover mysteries about the chapter's past. The Blood Ravens have been ordered to purge the planet in order to ensure the secrecy of their findings. They warn Alexander to leave, but he is determined to follow through with his orders and push the other factions off Kronus. Alexander is armed with Power Claws and wrist-mounted Bolter. Once fully upgraded he wears a wrist-mounted plasma pistol and powerfists as well as a full suit of carapace armour.
Should the Governor-Militant be successful in his task, he will become one of the most powerful men in the galaxy with an entire planet at his command, loyal Guardsmen, a Hellstorm cannon, and a debt owed by the techpriests of Adeptus Mechanicus. He will, however, have gained an enemy in the form of the Blood Ravens, who will probably be too busy defending themselves in front of the Inquisition.
When the Imperial Guard finishes off the other seven races in Dark Crusade, most of the 1st Kronus Regiment is sent off world to other battlefields while Lukas Alexander stays behind to oversee the creation of a new government and train the new PDF. The Adeptus Mechanicus is grateful to Alexander for defending them while they completed their study of the Hellstorm Cannon. The human population that had chafed so long (apparently) under Tau control rose up and murdered every single Tau once Alexander destroys the Tau stronghold. His men have seized documents from the Blood Raven's razed Castellum Incorruptus in North Vandea that shows previous visits to the planet and shocking gaps and contradictions in the Chapter's history - which calls into question the true nature of the Blood Ravens.