Astonishing as it is to consider, the Doom series is pushing 30 years old. The first game was released in 1993 and quickly became the first great rock star of the (at the time) brand new first-person shooter genre. It's even weirder to note that, since 1993, there have only been six core games in the series up to 2020's Doom Eternal, or seven if you count Final Doom.
Nevertheless, despite the relatively few Doom games around, they pack some of the hardest fights and the toughest bosses in any FPS. Some Doom bosses are so iconic they even come back for an encore, and players have to kill them all over again.
Hell Guards (Doom 2016)
This boss in the 2016 reboot of Doom is actually one of the few enemy boss teams the player faces in the series, as there are three of them to defeat. They are the guardians of the Crucible sword and responsible for one of the biggest shocks in the game, as facing one of them is bad enough. The player struggles to defeat the first, then two show up at the same time. The Guards are suits of crab-like armor worn by a tiny worm parasite, and they take some real strategy to defeat, as they're quicker than other bosses and have some mean area attacks.
Sabaoth (Doom 3)
This boss appears around the mid-point of Doom 3, and it's a bit of a tragic one. Throughout the game up to this point, the Doom marine had been trying to meet up with his commander Sergeant Kelly, who's been helping him since the initial demon invasion. Unfortunately, as the player nears Central Processing it becomes clear that something has happened to Kelly. They finally discover that the sergeant has become a tank-like cyborg called Sabaoth. The player has to fight the hulking monstrosity in a tiny area filled with electric traps and sheer drops, and Sabaoth is armed with the BFG-9000. The good news is that, once Kelly is dead, the BFG can be picked up.
Mother Of All Demons (Doom 64)
While for the most part Doom 64 contains the same set of demons as regular Doom, the final boss is something wholly unique and deeply unsettling. The Mother Demon screams like a banshee when the player first sees her and continues to make creepy noises throughout the tough fight. The Mother Demon fight is also one of the few boss battles in the series that can change depending on how the player performed.
If the player was diligent enough to find the keys throughout the game to unlock the Unmaker gun, the Mother Demon is relatively easy. If not, she becomes one of the toughest fights in the Doom series.
Vagary (Doom 3)
The first boss of Doom 3 isn't particularly difficult nor requires any special strategy, but it is probably the most terrifying and memorable. Right up until the player encounters her, they discover cobweb-strewn hallways, spider creatures, strange noises, and scary voices. When they finally enter the Vagary's lair, they discover a hideously mutated naked woman grafted to a spider body. Slightly reminiscent of Quake's Vore monster, it's deeply disturbing and is rendered worse by the creature having telekinesis powers.
Samur Maykr/The Seraphim (Doom Eternal: The Ancient Gods)
Doom Eternal's first expansion, The Ancient Gods Part 1, is the toughest challenge in the Doom series. Consequently, the final boss of the DLC is incredibly stressful, but definitely memorable. Samuel Hayden, the on-again-off-again ally or antagonist since the beginning of Doom 2016, gets killed in Eternal and is finally resurrected as the Seraphim Samur Maykr. The fight takes place in a constantly changing room with raising platforms and many environmental traps, with a Seraphim who keeps teleporting and many demons to support him, which makes the fight a lot tougher.
Maledict (Doom 3: Resurrection Of Evil)
At the end of Doom 3, the player sees the fate of antagonist Dr. Malcolm Betruger, who was swallowed by a skeletal dragon in the depths of Hell. In the expansion DLC Resurrection of Evil, Betruger has become fused with the creature, becoming the final boss of the whole Doom 3 saga. The player is trapped on a single platform as the dragon flies and swoops in, attacking from all sides with fire attacks. Maledict is tough, but the player can and should use the time-slowing Artifact to stop the creature in its tracks. Just don't expect an ending after defeating Maledict, because there isn't one.
The Khan Maykr (Doom Eternal)
The supreme ruler of Doom Eternal's twisted version of Heaven isn't an ally of the Doom Slayer or humanity and is actually the one responsible for unleashing Hell on Earth. As the Slayer stops her evil plans she instead resurrects the titanic Icon of Sin, but the Slayer interferes with that too, and inadvertently allows Hell to invade Heaven/Urdak.
The Khan Maykr finally turns on the Slayer, and an epic battle ensues. Aside from fiery blasts, the player has to contend with endless Maykr drones and the floor getting progressively more dangerous, making this one of the toughest fights in the Doom games.
The Spider Mastermind (Doom/Doom 2016)
The original final boss of the Doom series, the Spider Mastermind is the leader and strategist of Hell's forces and seems to be the current Dark Lord until the Slayer kills it. It's a demon with a huge brain attached to four cybernetic spider legs. The original is armed with a powerful chaingun. The reboot has a plasma cannon, lasers, and the ability to electrify the floor. While not the most powerful demon around, the Mastermind's status as the final boss of Doom ensures it'll be an enemy long remembered.
Icon Of Sin (Doom II/Doom Eternal)
The Icon of Sin is the final boss of both Doom II and Doom Eternal, and they could not be more different, despite supposedly being the same thing. The Icon originally appeared as just a Baphomet-like head that continuously spawned demons, which is how it appeared in its Doom 2016 cameo. In Doom Eternal, however, players finally see the Icon's body, and it's a towering colossus that lays waste to skyscrapers. The Icon is one of the best fights in FPS history, forcing players to avoid constant regular demons while collecting ammo to take out the Icon of Sin's armor and body parts. It's tense, adrenaline-filled, and deeply satisfying.
Cyberdemon (Doom/Doom 64/Doom 3/Doom 2016)
Doom's iconic Cyberdemon has been the most memorable boss in four of the series' games and has appeared in some fashion in the other Doom titles too. In general, the Cyberdemon's appearance and fighting style don't change: it's a giant horned demon with a clunking robot leg and a powerful rocket launcher for an arm. The Doom and Doom 64 versions could kill the player with a single hit. The Doom 3 final boss was immune to the Doom Marine's weapons, and could only be hurt with the Soul Cube. The 2016 version is teased throughout the entire game and is far more deadly and agile than previous appearances. Whenever the Cyberdemon appears in Doom, players know they're in for the fight of their lives.