Lukash is the leader of the Freedom faction and he can be found on the top floor of the main building at the Freedom HQ in the Army Warehouses area. He can provide you with a number of optional missions. The most notable mission is Destroy the Duty company that requires you, with the help of some Freedom members, to take down all the Duty members at the nearby outpost; the mission is followed up with Deal with the snitch, and completing them both with provide you with 7000 RU - and, as a side bonus, Skinflint will be selling more and better equipment.
He is the leader of the Freedom organization. As you’ve probably suspected, you will be able to receive main Freedom quests from him. Also, killing him will be one of the main goals of the Duty organization.