"What a MOOvelous occasion!"— The Cow King(src)
In Diablo II, the Cow King is the Super Unique boss of The Secret Cow Level. It looks just like any other Hell Bovine: there aren't any visual clues to identify it, except highlighting. However, the Cow King always spawns inside the fenced enclosure located in the secret cow level, so players who wish to avoid killing him can just avoid the enclosure altogether.
The Cow King is the only creature in the entirety of Diablo II to drop "The Cow King's Leathers".
Once he is killed, the portal to the Secret Cow Level cannot be opened again in the same difficulty. So, that makes the Cow King's Leathers the hardest set to complete in one game because there are 3 set pieces and the player gets only 3 chances to kill the King - one in each Difficulty. This results in a popular tactic among those that wish to run the level to avoid slaying him at all costs. Deliberately killing The Cow King while in a party is often considered a major offense.
Besides these two attributes that always appear, the Cow King gains one additional attribute (random modifier) on Nightmare and two on Hell. One of the most annoying attribute that it can get is Aura Enchanted: a Conviction aura Cow King coupled with its natural lightning enchanted can make fighting the Cow King a very hazardous task. It can also hold a range of immunities which can be quite annoying for pure-elemental Sorceresses and other element-dependent characters.
The Cow King is known more for his infamy among the rumor mills than for his drops. Ever since his discovery as an easter egg, he has been associated with various other fake hidden eggs. He was supposed to:
- Be able to drop the Bovine Armor unique item from Diablo: Hellfire
- Be able to grant access to a hidden Hireling - the Angel in Act IV
- Be related to Lester the Farmer from Hellfire
An NPC called "Ghost of the Cow King" appears in the Old Tristram Road in Diablo III, next to the portal to the Pony Level (the game's Cow Level). The ghost refers to the "fact" that there is "no cow level" after the player character breaks the fourth wall by referring to said level about cows.
Nephalem Rifts has a very small chance to have a Rift Guardian named Lord of Bells, who takes the form of a huge cow with a two-handed axe, clearly a reference to Cow King. In addition, players may find (and use) his weapons: Bovine Bardiche and Man Prodder.
A non-combat pet named That Which Must Not be Named can be found in game.
- The Cow King has a male voice (and title), and is overall regarded as a male. However, it has an udder and has been stated to produce milk.. To add even more confusion about the Cow King's gender, two different creatures named The Cow Princess and The Cow Queen can be encountered in Diablo III, and neither of them is the Cow King (as his ghost can still be seen in the same level). The gender of these two creatures is unknown, as they never speak, and no other in-game characters speak of them, neither as 'him' nor as 'her'.