Jagar Tharn (Reign of Chaos)

Jagar Tharn is an Imperial Battlemage who overthrows Uriel Septim VII and banishes him to a plane of Oblivion, along with Talin Warhaft I. He possesses the ruby throne in Reign of Chaos and takes the Emperor's form, he has Talin Warhaft's son thrown in the dungeon. Tharn continues to rule Tamriel, currently aware that Talin has escaped and that he and his band of prisoners plan to overthrow him.

Background
Little is known about Tharn's past, other than the fact that he became an Imperial Battlemage to the Emperor. However, his past is unknown, according to the book 'The Real Barenziah' he is apparently of Bosmeri, Dunmeri and Altmeri lineage mixed with Imperial Ancestry.

Tharn's betrayal
It is unknown when Jagar decided to betray the Emperor, though it must have been long before he did so as he stole the Staff of Chaos from a sanctuary, beneath the city of Mournhold. It is unknown if he did this himself or if he sent and agent.

Tharn offers himself as an adviser to the Ruby Throne and acted as a counter to Septim's ambitious and plans of aggressive expansion. They later formed a master-pupil relationship and the Emperor benefited from Tharn's power and wisdom.

The Half-Breed eventually met with the Emperor and used the staff of Chaos to Imprison him and Talin Warhaft I in a realm where they experienced nothing but endless horrifying nightmares. Time moved slower in that realm than it did in the realm of Mundus and, as a result, it would take centuries for the Emperor to die, allowing Tharn to rule comfortably for several years.

Tharn went on to drain the staff of chaos and shattered it, to prevent anyone from releasing the Emperor. He scattered them across Tamriel, in dangerous or inaccessible places to make it impossible for them to be recovered. He then dismissed the Emperor's inner circle and replaced them with his own loyal subordinates.

Several people who proved to be a threat to Tharn's rule were captured and several were even killed, Ria Silmane, his apprentice. Ria learned of his plans and attempted to inform the Elder Council but was killed before she could do so, however, not even death could stop such a powerful mage...

Reign of Chaos
Tharn is mentioned numerous times during the events of Reign of Chaos, Ria mentions him as she explains his plans to Talin. He later relays these plans back to the others...

Reign of Chaos: Chapter 1 - High Rock: Glenumbra
Tharn makes his first physical appearance (not counting the introduction) in this chapter as he invites Veranus and several other Guardsman into a chamber beneath the Imperial Palace. He pretends to give a speech as the Emperor, though it is actually a distraction to hide the fact that he is actually forming a magical contraption around the guardsmen. It isn't long before he activates it, turning Veranus and the other Imperials into beasts that are bound to his will.

His Nordic right hand enters and informs him of the escape of his prisoners...

He is later seen in another scene, where he orders his Nordic right hand to deal with the problem of the escaped prisoners. She assures him that it won't be a problem and that they will likely fall to beasts on the side of the road first. Tharn agrees, seeming a little too confident of that possibility...

Appearances
Reign of Chaos: Prolouge - The Imperial Prison

Reign of Chaos: Chapter 1 - High Rock: Glenumbra