The Impostor Jagar Tharn betrayed
the Battlespire, the war college of the Imperial Battlemages,
to the legions of Daedra Lord Mehrunes Dagon. Two trainees
trapped in the Battlespire escaped by fighting their way
through daedric gates until they came to the citadel of
Lord Dagon, where, by a subtle trick, they cast the Daedra
Lord into Oblivion. Having lost Lord Dagon's support,
Jagar Tharn's plot to supplant the true Emperor was doomed
to fail.
"...for had not Jagar Tharn been
robbed of the support of the archfiend Mehrunes Dagon
and his fell minions, then Ria Silmane and her champion
might never have revealed Tharn's imposture, and long
might the rightful emperor have languished imprisoned
in Dagon's dark prisons within the Void."
- From THE CHRONICLES OF JANISIERE