Doom: The Dark Ages

=== Main campaign ===
At some point following his arrival on the planet Argent D'Nur and his subsequent empowerment, the Doom Slayer is weaponized by the alien Maykrs to assist Argent D'Nur's people, the Night Sentinels, in their war against the forces of Hell, who seek an object known as the Heart of Argent; the Slayer does not fight completely of his own free will, however, as his master, Kreed Maykr, suppresses him with a device called a Tether. Meanwhile, the leader of the demons, Prince Ahzrak, realizes it is not worth fighting the Slayer directly and focuses his efforts on finding the Heart.
Ahzrak finds the hiding place of the Heart, but the Slayer and King Novik manage to thwart him. However, Novik decides to keep the Heart with himself, not fully trusting the Slayer or the Maykrs. Ahzrak attacks the retreating Sentinel forces. Kreed refuses to deploy the Slayer to help them, intending to keep himself protected. Unwilling to let innocents die, the Slayer is able to break free of the Tether's control, forcing Kreed to send him back into battle, where he successfully holds off the demons long enough for the Sentinels to escape. Ahzrak is able to steal the Heart from Novik but finds it empty and useless. Ahzrak offers an alliance to Kreed, who himself has come to fear the Slayer turning on him. The Slayer attempts to remove the Tether from his armor with little success. Novik's daughter, Commander Thira, tasks him with finding the Heart's power source before Ahzrak does.
Thira invokes an ancient ritual to empower the Slayer's shield, and he assaults Ahzrak's fortress in Hell. Meanwhile, Kreed betrays the Sentinels by sending a recording of Thira's ritual to Ahzrak, who realizes that Thira is actually the Heart's power source, and orders her capture. Failing to find Ahzrak, the Slayer returns to Argent D'Nur only to see Thira and Kreed being taken by demons. In order to follow them, the Slayer reawakens an ancient being, known as an Old One, and follows it back to its homeworld, the Cosmic Realm. However, Kreed betrays the Slayer and Ahzrak overpowers him. Ahzrak reveals Thira houses the soul of a Wraith, who are descendants of the Cosmic Realm, and extracts it to power the Heart. Instead of following Kreed's advice to kill the Slayer since the latter cannot permanently die, Ahzrak instead leaves him imprisoned by the Old Ones while he leads the final assault against the Sentinels.
The Slayer self-destructs the Tether in his armor, killing himself. His soul is sent to Hell, where he fights his way back to the mortal plane as Commander Valen resurrects him with a demonic ritual. The Slayer kills Kreed, then confronts Ahzrak once again, defeating him and freeing Thira's soul. Ahzrak flees back to Hell, with the Slayer and Thira in pursuit. The Slayer kills Ahzrak, causing his forces to retreat. Afterwards, the Maykrs disavow Kreed's actions while Novik and Valen plan to purge any remaining traitors in their midst. Thira rallies the Sentinels, bidding them not to put their faith in the Maykrs, but in themselves instead. Meanwhile, the Slayer commandeers Kreed's ship to continue his crusade against Hell.



Revelations

The Slayer confronts Hell's High Council, but they use the Slayer's deep-seated guilt to weaken him, and he is defeated by their champion, the Henchman, and banished to a purgatory beneath their chamber. In the purgatory, the Slayer is found by the Architect, who nurses him back to health and repairs his weapons and shield. The Architect instructs the Slayer to collect three Ascension Stones that will cleanse his soul and allow him to escape. The stones reveal the source of the Slayer's guilt: back on Earth, when he was a MARSOC operative, the Slayer destroyed an enemy bunker beneath a hospital, but killed a young girl in the process by mistake; codex logs also reveal the Slayer assaulted his superior officer over the incident, as he was under the impression the hospital was devoid of civilians, leading to him being court-martialed and sent to perform grunt duty on Phobos.
The Slayer acquires a replica of Novik's axe, through which he sees Novik being killed by Valen's son, Marok—appointed as the champion of the Maykrs' leader, the Khan Maykr, who secretly allied with Hell and convinced them to stop attacking Argent D'Nur in return for betraying the Slayer. Marok arrives at the purgatory and destroys the Slayer's exit portal; the Slayer defeats Marok, who kills himself before his Tether can reassert control. The Architect turns the stones into a power source for the Slayer's new armor, the Praetor Suit—the suit that the Slayer would use in his later battles against Hell; the Praetor Suit reactivates the portal. The Slayer returns to Argent D'Nur, finding its populace on the brink of a civil war between Maykr loyalists and those who distrust them. He gives the replica to Thira; upon touching it, Thira sees her father's death and orders her forces to rebel against the Maykrs. The Khan Maykr retreats with the Night Sentinels still loyal to her, and summons the Henchman; the Slayer kills the Henchman, and Thira declares war on the Maykrs. In a post-credits scene, unlocked via completing all postgame content, Valen is tormented by demonic whispers; Thira arrives and offers him the axe replica.