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Mehrunes Dagon (in Daedric script: Daedric MDaedric EDaedric HDaedric RDaedric UDaedric NDaedric EDaedric SDaedric DDaedric ADaedric GDaedric ODaedric N) is one of the seventeen Daedric Princes of Oblivion and the primary antagonist of The Elder Scrolls IV: Oblivion.
Contents[show]
BackgroundEdit
His spheres are destruction, change, revolution, energy, and ambition. Mehrunes Dagon is the foe of all mortal races, and has attempted to conquer the physical world Nirn many times. The common reasoning behind his many plots is his belief that Tamriel is in fact a plane of Oblivion which is rightly his. He constantly invaded Tamriel relentlessly from the First Era onward.
The most famous of Dagon's invasions of Morrowind is certainly the attack on the capital city of Mournhold at the end of the First Era[1]. Dagon was defeated by the god-like Almalexia and Sotha Sil, but not before he destroyed the entire city and devoured its populace. Mehrunes Dagon was also behind the destruction of Ald Sotha, where he destroyed House Sotha. During the Imperial Simulacrum, in the years 3E 389-3E 399, Lord Dagon conspired with Uriel Septim VII's power hungry Battlemage Jagar Tharn to imprison the Emperor in Dagon's plane of Oblivion while Tharn assumed the Emperor's likeness and ruled in his place. Further, Dagon assisted Tharn by attacking the Imperial Battle College in the Battlespire.

This attempt at taking over Tamriel was stopped by a mere mortal. Brooding over his many defeats, Dagon eventually came up with his next attempt to conquer Tamriel. This attempt was to become known as the Oblivion Crisis. He had his Mythic Dawn cultists assassinate the Emperor and all of his heirs, but one was unknown, and survived. The heir, the Blades, and the Hero of Kvatch continually defeated him until the assault on the Imperial City, where Dagon was defeated and banished back to Oblivion by Akatosh himself.[2]

Plane of OblivionEdit
Mehrunes Dagon's plane of Oblivion is the Deadlands.
The Invasion Of MorrowindEdit
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"A gout of ever erupting flame was all that remained of the central courtyard of Castle Mournhold, blasting skyward into the boiling clouds."
?Carlovac Townway[src]
Lord Sotha Sil visited Coldharbour, following the destruction of the city of Gilverdale in Valenwood by Molag Bal. He made a deal with eight of the more prominent Daedric Princes: Azura, Boethiah, Hermaeus Mora, Hircine, Malacath, Mehrunes Dagon, Molag Bal and Sheogorath. The terms of the deal was that during the war between Morrowind and Cyrodiil, the Daedric Princes should not accept any summon by a mortal, unless it was done by witches or sorcerers.
However, a former spymaster of Vivec managed to summon Mehrunes Dagon by fueling the rage of a witch of the Skeffington Coven in High Rock. The witch wanted to take Revenge upon the Duke of Morrowind, while the spymaster just wanted to see Morrowind suffer after what Vivec had done to him. Mehrunes Dagon went further and destroyed Mournhold, the capital of Morrowind, in one of the most devastating attacks ever recorded by historians. Although Mehrunes Dagon was eventually banished back to Oblivion by a joined effort of Almalexia and Sotha Sil, Mournhold had been totally destroyed, and the Duke of Morrowind was slain. A new city was constructed right atop the ruins of the destroyed Mournhold.

Also in Morrowind, Dagon was responsible for the destruction of Ald Sotha, ancient home of the Dunmer House Sotha and reported birthplace of Sotha Sil. It is also likely here that the Forces of Destruction were somehow involved.

Imperial SimulacrumEdit
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"He was involved in Jagar Tharn's plot against the empire years ago."
?Jauffre[src]
During the Imperial Simulacrum, Jagar Tharn dealt with Mehrunes Dagon, and it is rumored that Molag Bal assisted in some way, although he did not help in the following events.
Assault to BattlespireEdit
Summary:
After the Miracle of Peace, when the great Numidium was resurrected and destroyed once again, Mehrunes Dagon attempted to invade Tamriel beginning with the fort Battlespire, where the imperial battlemages used to have their final test before graduating. An apprentice teleported to the floating fort for his final test. The unnamed apprentice wound up in middle of the daedric invasion. Then through purging the levels and traveling to the Oblivion planes, the unnamed apprentice frustrated Mehrunes Dagon's ambitions.
Details:
Mehrunes Dagon assaulted the Battlespire, a proving ground and bastion of the Imperial Battlemages. Tharn had to destroy the Imperial Battlemages to smoothen his rule over Tamriel in Uriel Septim VII's seat. However, the Prince of Destruction had a hidden agenda - he wanted to invade Tamriel. Since the Prince and his Daedric army could not cross into Tamriel directly, he conquered and used multiple pocket dimensions and the Battlespire, which was the final gateway, as the steps to the mortal realm. One of the invaded realms was Shade Perilous, one of the realms of the Daedric Prince Nocturnal. Two of Nocturnal's lieutenants, Deyanira Katrece and Jaciel Morgen severely suffered due to the invasion of Mehrunes Dagon.
Although the Battlespire had fallen; an unnamed apprentice managed to banish Mehrunes Dagon to Oblivion. The hero used Mehrunes Dagon's protonymic and neonymic; and then hit the Prince with the Daedric Broadsword of the Moon Reiver, an artifact of great power that was forged from Mehrunes Dagon's own essence. With this action, Mehrunes Dagon's anchor to the mortal realm was severed and he was banished to Oblivion. The Battlespire itself was destroyed after the banishment of Mehrunes Dagon, due to the fact that the magicka anchors that were supporting the floating citadel were also severed.

Another artifact that was worth being noted in this period of chaos was the Daedric Crescent Blade. These Blades were used in the invasion of Battlespire by Mehrunes Dagon's army. After the event though, the Septim Dynasty declared this weapon illegal, and thus made the blade highly prized among collectors.

Oblivion CrisisEdit
RuinedKvatch
The ruins of Kvatch.
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"We have been preparing for the coming of Lord Dagon for many months now. The time of preparation is almost over, the time of cleansing is nigh."
?Mythic Dawn agent[src]
In the last years of the Third Era of Tamriel, Mehrunes Dagon formed an allegiance with the Altmer wizard Mankar Camoran. Dagon presented Camoran with his book of razors, the Mysterium Xarxes, the principles of which Camoran used to found the Order of the Mythic Dawn, a daedric cult devoted to the destruction of the Septim bloodline and the re-creation of the mythic era in which they believed Dagon would rule.
Certainly the most famous show of power from the Daedric Forces of Destruction was during the Oblivion Crisis, where Mehrunes Dagon sought to conquer all of Tamriel. In order for Dagon's Forces to invade, however, the Emperor and his heirs had to be removed. This task fell to the Mythic Dawn, who succeeded in assassinating Emperor Uriel Septim VII. This doused the divine Dragonfires and allowed Gates to Oblivion to be opened all across Tamriel. The first attack made by the Daedra was on the city of Kvatch. Following the Battle of Kvatch, Oblivion Gates were opened in earnest by the Mythic Dawn, allowing the Daedra to roam the countryside while the main army focused on attacking the major cities.

DaedraEmerge
The Daedra emerge.
This invasion was to be foiled by the combined efforts of the last surviving heir to the throne, Martin Septim, and the anonymous Hero of Kvatch. Time and again, the Hero took the battle into Oblivion itself, fighting off the Daedric Forces of Destruction. After a particularly harrowing defeat at the city of Bruma, as well as the fall of the Mythic Dawn during the Hero's raid on Mythic Dawn leader Mankar Camoran's realm of Gaiar Alata, the Daedra launched a final assault on the Imperial City.
Light the Dragonfires Mehrunes Dagon
Mehrunes Dagon invades the Imperial City.
Here, Dagon himself entered the fray, in an attempt to stop Martin Septim re-lighting the Dragonfires.[3] But it was to no avail; using the magical Amulet of Kings, Martin summoned/merged with Akatosh and banished Dagon back into Oblivion, and with him the whole of the Daedric Forces of Destruction.
This act, however, consumed both Martin himself and the Amulet but apparently rendered the Dragonfires and the Septim Bloodline redundant anyway so Tamriel no longer required the institution of the Empire. Presumably Akatosh's direct intervention, infused with the life-force of a living Septim, tied the wards that kept Oblivion separate from Nirn to the Divine realm rather than the mundane.

In the southern regions of Cyrodiil, there existed the Nefarivigum, a foul construct of Mehrunes Dagon, that was erected to be ever watchful for the pilgrim who would approach it and best an unknown trial of worth. It was said that such a pilgrim would be rewarded with the blessing of Mehrunes' Razor. It seems that the construct was able to retrieve the razor from its current owner, and give it to the pilgrim that finished the trial.

The Ayleids tried to prevent the blade from being released; therefore they erected Varsa Baalim, a city that surrounded the Nefarivigum. After so many years the city stood strong; however, some unfortunate events occurred, and the city was destroyed and lost from the annals of history. Sometime during the Oblivion Crisis, Frathen Drothan, a rogue Telvanni tried to retrieve the blade in order to support his rebellion against the Septim Empire. He found the ruin of Varsa Baalim, and eventually he reached the Nefarivigum; however, the Hero of Kvatch thwarted his evil and retrieved the blade for himself.