Axe Cleave	He'll do this if he's reasonably close enough to you to hit. He's quite fast on the draw here and thus very hard to avoid or defend against. Best to keep away from him until casting a spell to avoid this.
Hammer Pound	As with the Axe Cleave, this comes fast but has a bit of a lag time so you can catch him and thus avoid the attack. If you do get smashed, you are stunned briefly, in which case his cohorts can come in and tear you up. Best to keep away from him until casting a spell to avoid this.
Dizzy Swirl	If you manage to get too close to the brute, he'll swing around in an almost impossible to dodge swirl thrusting you back and stunning you; thus accentuating the point of staying away from him when he's not casting a spell.
Fire	His spell of choice is also his weakness. He'll stop often and cast quick fire spells under your feet. Best to keep moving in this battle and cast a spell of your own back at him.
Self Destruct	When he gets extremely low on health, he'll stop and start glowing bright. You only have around 20 seconds or so to either eliminate the rest of his health completely or run as far away as you can before he explodes damaging you greatly.

Later Cycles: In the later cycles, his Orc minions will come out in full force and be much stronger. The Orc King himself will get a major boost in statistics and be more dangerous than before. Not only will he employ Fira spells, he'll cast them faster than ever before in cycle 3. His self destruct mode activates sooner leaving you with more health to knock off before he expires; its best to simply run to the far side of the room for this.