He is a decisive man, and is part of a line of secret Daedric worshippers, which is just one more reason why the Alliances wish to dispose of him. He is working with the Necromancer Lord Mannimarco in order to combine Nirn with Coldharbour, Molag Bal's Daedric Realm, after realizing the threat posed by the Ebonheart Pact, Aldmeri Dominion and Daggerfall Covenant. 
Chronicles of the Five Companions- Tharn Edit
I am Grand Chancellor Abnur Tharn, Overlord of Nibenay, the head of the Elder Council, advisor to kings and emperors for one hundred and seventeen of the one hundred and sixty-four years I have been alive. I did not come by my postion of influence by luck or nepotism, but rather through extreme discipline, ambition and cunning. And yet, here I am, conspiring with idiots and fools in a musty hole in the ground. How the mighty have fallen.
...We Tharns have held postions of power in Cyrodiil since the days of the Potentate. We are prized for our loyalty to the Empire, our deft political machinations, and our ruthless subjugation or elimination of dissenters within Imperial territories. What we do is grim work, but it is necessary if the Empire is to endure.
Do I sound boastful and egotistical? Perhaps I am.