Mehrunes Dagon

"When I will walk the earth again, the Faithful among you shall receive your reward: to be set above all other mortals forever. As for the rest: the weak shall be winnowed: the timid shall be cast down: the mighty shall tremble at my feet and pray for pardon."

- Mehrunes Dagon.

Mehrunes Dagon is the primary antagonist in The Elder Scrolls IV: Oblivion, and one of the sixteen Daedric Princes, demonic deities who each have their own parallel dimension to rule over, which are collectively known as the "Oblivion". His sphere of influence is destruction, change and ambition. He is also the second most evil Daedra prince and the most dangerous, and his plane of Oblivion, the "Deadlands", resembles Hell and is inhabited by an army of demonic creatures called Dremora. His goal is to take over the mortal world, which he has attempted several times.

Elder Scrolls IV: Oblivion
During the events of Oblivion, a cult called the Mythic Dawn attempts to summon Mehrunes Dagon and opening gateways into his plane of Oblivion throughout the kingdom. Their plan involves destroying the royal bloodline by killing King Uriel Septim and all his sons, which they succeed in except for one, his illegitimate son Martin. Before his death, the Emperor frees a prisoner in the palace dungeons (the player) and tells them that he saw them in his dreams and want them to find Martin to stop the Daedra invasion.

The hero finds Martin, and together they lead a campaign to destroy the main Oblivion gates and gather the artifacts needed to stop the Mythic Dawn. Eventually, they gain access to the cult's headquarters in the alternate dimension of "Paradise", and kill its leader Mankar Camoran. After that, the last thing left to do is for Martin to be officially crowned as the new Emperor and light the sacred "Dragonfires" in the Imperial City's temple to stop Dagon from appearing in Tamriel. However, Mehrunes Dagon is summoned into the middle of the city before they can do so, thus completely severing the barriers between Tamriel and Oblivion made by the Dragonfires. As a last resortm Martin sacrifices himself inside the temple to summon a giant flaming dragon, the avatar of Akatosh the god of time, to banish Dagon to Oblivion forever.

Elder Scrolls V: Skyrim
In Skyrim, there is a giant shrine to Mehrunes Dagon. A descendent of one of the Mythic Dawn members who is historically fascinated and obsessed with the cult has the player gather for him the scattered pieces of Mehrunes Razor, and the pieces are then brought to the shrine to be assembled. Mehrunes Dagon's voice then tells the player to kill him in order to be rewarded with the reassembled razor.

Divine & Daedric Peers
For his breaking of pacts with the Aedra and actually appearing on the plane of Mundus during the events of Oblivion even while the Amulet of Kings was held by Martin: the descendant of Akatosh, Akatosh himself smote Dagon as previously mentioned. This would mark Maehrunes Dagon as an enemy of the Aedra and his followers were hunted down by all followers of the gods; however this was not the only consquence. The other Daedric Princes all despised Dagon even more than the the Aedra, for while the Gods objected to Dagon's contempt for the world, the Princes objected to Dagon's contempt for their credibility. The pact made with the Aedra to not directly affect Mundus was not made just between Dagon and the Aedra but in-fact between all the Daedric Princes and the Aedra, so in breaking his oath, Mehrunes Dagon had damaged the creditability of all his brethren. While the mortal followers of the Aedra branded Mehrunes Dagon's followers as heretics and criminals the, Daedric Princes, whose followers might otherwise have offered sanctuary to their fellow cultists, turned their backs on the members of the Mythic Dawn and indeed forsook Mehrunes Dagon as a Daedra worthy of any reverence. All the Daedric Princes are theorized to have had a hand in rendering Dagon a forsaken god, and thus responsible for his seeming obsolescence during the events of Skyrim. Meridia, Sheogorath, Boethiah, and even Molag Bal, have all stated their utter contempt for Mehrunes Dagon prior to the events of Oblivion and so it is all but certain all consider him even more wretched currently.