Bosses

"Bosses" is an all-encompassing word that is often used to describe any overpowered single enemies who must be killed to progress in game, and cannot be avoided, but most of the time Act Bosses are meant by bosses. Unique Monsters and Super Uniques are also often included.

Gameplay
A boss fight is usually set in a specific location, with limited space to kite them. Often it will be very hard, if not impossible, to use a Town Portal, so preparation is advised. In Diablo III, every boss fight takes place in an isolated chamber, and once it has started, there is no escape: the combat will not end until either side prevails. No mercy, no escape. Death or glory. Even to start a boss fight, all players in a group must click the "Yes" button. However, Rift Guardian bosses are spawned in usual locations, and it is possible (nobody said "easy") to escape the battle with them.

Bosses are characterized by their massive amounts of Life, many unique abilities they do not hesitate to use in combat (some of them capable of one-shot killing a hero, but usually boss skills are predictable and can be avoided), as well as increased damage. Many bosses are also assisted by hordes of minions, and may summon more at will.

Overall, boss fights are focused on player skill rather than raw damage per second and damage control, so players need to put all their effort into fight (unless, of course, they are way too overpowered for that boss and difficulty).

All bosses in Diablo II count as Super Unique Monsters, and all bosses in Diablo I and Diablo III are Unique Monsters, indicated by the color of their names.

In Diablo III, many bosses have an Enrage Timer.

Diablo IV includes a stagger system for some monsters, including bosses. Players can induce control effects on bosses, and in doing so, this fills up their stagger bar. When it fills, the boss becomes staggered.

Diablo I

 * The Defiler
 * Na-Krul
 * Lazarus
 * (final boss)
 * (final boss)

Diablo II

 * Andariel
 * Duriel
 * Mephisto
 * Baal
 * Baal

Quest monsters like Zhar the Mad, Warlord of Blood, Countess, Blood Raven or the Summoner can be regarded as bosses.

Diablo Immortal

 * Acolyte of Damnation
 * Baal
 * Blood Rose
 * Bloodsworn Priestess Innaloth
 * Cold Snap
 * Corphet the Venomwing
 * Elder Owen
 * Eskara
 * Fallen War Matron
 * Grimaldi the Flaming Soul
 * Icon of Rebirth
 * Icon of Souls
 * Ifriss the Destroyer
 * King Fahir
 * Lakrii
 * Manoruk
 * Purus the Decimator
 * Rhodri the Red
 * Sargoth
 * Segithis
 * Siegebreaker Assault Beast
 * Sir Gorash
 * Skarn
 * Skeletal Mage
 * Skeleton King
 * Skorspine the Tarrowrot
 * Soul Killer Shaman
 * The Countess
 * The Curator
 * The Eternal Guardian
 * Ventar the Unholy
 * Zaka

Diablo III

 * (King Leoric)
 * Queen Araneae
 * The Butcher (act boss)
 * Maghda
 * Zoltun Kulle
 * Belial (act boss)
 * Ghom
 * Siegebreaker Assault Beast
 * Cydaea
 * Azmodan (act boss)
 * Iskatu
 * Rakanoth
 * Izual
 * Diablo, the Prime Evil (act boss)
 * Urzael
 * Adria
 * Greed
 * Vidian
 * Malthael (act boss)
 * Uber Bosses, including Infernal Machine and Pandemonium Event
 * All Rift Guardians
 * All Keywardens (Odeg, Xah'Rith, Nekarat and Sokahr)

Diablo IV

 * Ashava the Pestilent (world boss)
 * Blood Bishop
 * Skeleton Lord

Trivia

 * In Diablo III, a mode was experimented with where the player would control a boss, fighting against four enemy heroes.