The first actual boss you face in Diablo III, The Skeleton King is also a harkening back to the original Diablo, in which he was a surprise boss who only sometimes appeared. The dead King Leoric in that game was a terrifying melee monster, found in the middle levels of the Cathedral underground, who would constantly spawn extra skeletons and bash you to pieces.
His incarnation in Diablo III is both more and less worrying.
The Skeleton King basically does four things- two of these things are very Barbarian things, but the other two are more what you would expect from a lich-necromancer of some sort.
The first thing the Skeleton King tends to do is whirlwind. Extending his sword out and spinning, he will whirl towards a player, causing continual damage to anyone unlucky enough to be near him. This habit of his in particular makes it difficult to get through the fight without getting hit for a Barbarian player- fortunately, if you’re a Barbarian you’re tough enough to take a few of these and keep going pretty easily. This also only really applies in Normal mode- at higher levels, Barbarians have enough ranged capability to avoid this if they like.
The second thing the Skeleton King does is bash with his giant sword. This only deals damage, however, and while it is fearsome to a ranged character, who usually hasn’t got the defenses to withstand the strike, it is also slow enough that a ranged character shouldn’t usually be too close to run away.
The Skeleton King’s third tactic is to drop a summoning ‘gleam’, which creates several skeletons over a few seconds. This is more annoying than anything else, as the skeletons created by it aren’t anything remarkable- just more grunts. Standard area attacks will take care of this, or dropping a damaging zone effect when he starts the summoning. Wizards with Explosive Bolt rune and Barbarians with the exploding Cleave effect will find this especially easy to handle.
The one truly aggravating thing the Skeleton King does is to teleport. Fortunately for those in a party, he’ll teleport to whoever has the most aggro from him- usually the Barbarian if there is one. However, this usually is followed up immediately by a Whirlwind or an overhand strike with the King’s sword. Ranged characters need to have a teleport, evasion, or temporary invulnerability ready at all times just in case if they’re in a party. Those facing the Skeleton King alone will need to rely on the Templar, who unfortunately lacks his ‘taunt’ effects at this level, and thus is unlikely to draw the aggro off of you.
The best recommendation here is to run every time the King gets near if you’re ranged, and otherwise unload on him. Ranged characters will like their area attacks for his summons and their slowing and crippling effects for his Whirlwind and teleporting-smash tendencies. Otherwise, he is sadly nothing special.
Poor King Leoric.