Instructions
Build a balanced party. While it may seem a good idea to send in nothing but heavy hitters, the Ogre Alpha is no slouch in combat and can deliver very punishing attacks. Your ideal party configuration, which includes your own character in any of the mentioned roles, should consist of a heavily armored and defensive "tank" melee fighter, a mage, another ranged attack and another melee attacker. If the mage has healing spells, they will have increased utility compared to those of other characters. Otherwise, you'll need to rely on healing poultices to stay alive.
Maintain a sizable stock of healing poultices for the encounter. Even with a healing mage in the party, there may be times when there's too much damage for them to effectively heal by themselves. Having a stock of poultices enables you to have emergency healing when necessary, and a backup means of healing if your mage is killed during the battle. If your mage doesn't have any healing spells, these poultices will be your primary source of healing and you'll need to stay focused in order to stay alive.
Keep the Ogre Alpha focused on your tank. You'll want to bring a heavily armored character into the battle to serve as the "tank." The tank's job is to dominate enemy attention and soak damage while staying alive as long as possible. Ideally, your tank will be a warrior in heavy armor with sword and shield and spells to maintain enemy attention like Taunt. Your tank will need to mitigate damage actively through dodging with a heavily dexterity-based build or soak the damage by the sheer amount of health via a constitution-heavy build.
Keep the tank alive through healing spells or poultices. By commanding the Ogre Alpha's attention, the tank is going to be taking a considerable amount of damage. Because of this, they will need dedicated healing during the fight -- particularly when the Ogre Alpha uses hard-hitting attacks. The Ogre Alpha also has a move wherein he grabs the focus of his attention and pummels them into the ground for considerable damage. The tank's survival is of vital importance to the success of the fight: should the tank die, your other characters may not be sufficiently durable enough to withstand sustained punishment by the Ogre.
Wear down the Ogre Alpha. These beasts are essentially bosses, and as such they have considerable health -- they will not die quickly or easily. Keep your ranged attackers hitting hard, with your mage casting damage spells whenever they aren't immediately needed for healing. Keep your melee fighter also hitting with their most powerful abilities, so long as they don't break the tank's hold of the Ogre's attention or "aggro." While the battle may wear on for some time, diligence in healing, maintaining tank aggro and hitting the boss with all your most potent abilities will eventually pay off and lead to victory.