The Warden

The Warden is a mini-boss in Act I of Diablo III. He's a giant skeleton that the player must kill in order to loot the Warden's Key.

Summoning the Warden

The Warden must be summoned. He is a miniboss that exists inside of the quest to kill the Mad King Leoric. The relevant portion of the quest line is given to players by Queen Alyssa, the beheaded bride of Leoric. She resides in the entryway of the Torture Chambers of the Mad King, informing the player that they must free the spirits of her former servants who will not know peace until the hero shows up to liberate them. The liberation of the ghosts is the trigger to summon the Warden.

Flux wrote about this portion of the questline during his hands-on from BlizzCon 2010:

The player appeared in a narrow hallway, immediately before the spectral form of Queen Alyssa.

The quest was simple; you had to move through the fairly huge dungeon and find the six prisoners, then click them to set them free. The only difficulty for this was the size of the dungeon. It was quite large, but easy to move around since the passages were wide, straight, and regular.

The Warden in Combat

The Warden spawns in the middle of a cross-shaped intersection of flooring within the torture chambers, with steep drop-offs which ghouls will climb up to attack the player. The spawning of the Warden will be preceded by an omnipresent voiceover within the game, where he says "Am I alone here? Must I do this myself? So be it. Face me, and repent". Once the voiceover ends, the Warden will pop up in the center of the cross-shaped area to attack the player.

Flux also commented on this fight:

The Warden wasn’t hard; I never struggled to kill him off, or to stay alive while doing so, but he was fun. The battle is shown in the gameplay movie, which you should watch now if you have somehow not yet done so. The location is the crossroads in the center of the level, and once you reached it, after freeing all of the ghosts, hordes of ghouls can scrambling up the sides of the platform, and the Warden bellowed his powerful dialogue, before appearing, ready to smash.

The battle was best fought from one side, and a wise player stayed in the center only long enough for the spawn to begin, then retreated down one of the four paths. I did that with a Demon Hunter, Vaulting through the ghouls, and had a very easy time with it. All of the enemies had to come along the narrow path towards me, which made Entangling Shot very effective at hopelessly clogging their advance, while Multishot pierced through the mob, dealing damage to dozens of enemies per blast.

The Warden himself had a big stick and liked to hammer with it, but even when he whacked my Monk it wasn’t very heavy damage, and I had no real trouble punching the rest of his puny minions to bits.