Abnur Tharn is father to Clivia Tharn, the Empress Regent of Tamriel. He is known as High Chancellor and Overlord Of Nibenay, he is an original member of the Five Companions, and also the Imperial Battlemage of the Elder Council. 
Abnur is 164 years old and has at least 16 children. He most likely extended his lifespan through necromancy.
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. His family 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.  However, Abnur, despite sharing his family's traditions of Daedra worship, despises Mannimarco due to his involvement in the Soulburst.
He is the ancestor of Third Era Imperial Battlemage, Jagar Tharn, the progenitor of the Imperial Simulacrum who ruled the Empire for 10 years before the Eternal Champion freed Uriel Septim VII from Jagar's prison.
Chronicles of the Five Companions. Edit
After Abnur infused the Vestige with divine power with the Amulet of Kings, he helped the remaining Companions reach safety. After this he fled with the Amulet of Kings and returned to the Imperial City to attempt to harness the Amulet's power. According to Meridia, the relic's power will be dormant for several generations, and Abnur will not succeed, but will try nonetheless.