'Empress Katariah (?b - http://www.uesp.net/wiki/Lore:Third_Era#3E_200)
Wife of the eccentric http://www.uesp.net/wiki/Lore:Pelagius_Septim_III, Katariah was finally awarded the regency of Tamriel in http://www.uesp.net/wiki/Lore:Third_Era#3E_153. The Empress Regent of Tamriel was proclaimed Empress Katariah I upon the death of her husband. Some who do not mark the end of the Septim bloodline with the death of Kintyra II consider the ascendancy of this dark elf woman as the true mark. Her defenders assert that though Katariah was not descended from http://www.uesp.net/wiki/Lore:Tiber_Septim, the son she had with Pelagius, was, so the chain did continue. Despite the racist assertions to the contrary, Katariah's forty-six year reign was one of the most glorious in Tamriel's history. Uncomfortable in the Imperial City, Katariah traveled extensively throughout the Empire, such as no Emperor ever had since Tiber's day. She repaired much of the damage the broken alliances and bungled diplomacy had created. The people of Tamriel came to love their Empress far more than the nobility did.
Katariah's death in a minor skirmish in http://www.uesp.net/wiki/Lore:Black_Marsh in http://www.uesp.net/wiki/Lore:Third_Era#3E_200 is a favorite source for conspiracy-minded historians. The sage http://www.uesp.net/wiki/Lore:Montalius discovery of a disenfranchised branch of the Septim family's involvement with the skirmish was a revelation indeed. Her son, http://www.uesp.net/wiki/Lore:Cassynder, assumed the throne.'
From uesp.net
She's only mentioned in a book but I love her.

She's not necessarily my favourite but I wanted to mention her.