Lotharius was the Prince of Vienna during the Dark Ages. A childe of Etrius, he was responsible for the transportation of Tremere's torpid body to Vienna and was also among the first assembled Primogen of Jürgen of Madgeburg.
Born in 984 in Cologne, he was inducted to the Order of Hermes at the age of eight. He quickly rose through the ranks and became one of the order's youngest masters, before he started travelling the lands as a diplomat for the Order. In 1012, he befriended Etrius who introduced him to House Tremere.
During his stay in Ceoris, he vanished because of a magical accident for twenty years and when he returned, the House had started to adopt vampirism in order to escape their weakening magic.
He reluctantly accepted the Embrace from Etrius, and afterward traveled the world again, acting as a diplomat for the new clan and to hunt Salubri. In 1032, he was made Pontifex of Austria and tasked to form it into a base of power for the clan.
He quickly usurped control over Vienna from the previous prince, Valerianus, and transformed Vienna into the bastion of power that the Tremere has kept until this day. Most of his concerns, however, were focused on the Tzimisce and the growing influence of their methuselah, Shaagra.
When Tremere's torpid body was relocated to Vienna, Lotharius stepped down from his princedom, making way for the privy council that would rule Vienna instead. Lotharius was part of this council for several years, before he was assassinated by an Assamite in 1529.
According to the German-language sourcebook Wiener Blut: Wien Bei Nacht, produced under license by Feder & Schwert, Lotharius usurped control of Vienna from Valerianus in 1351. This source was referenced in Encyclopaedia Vampirica, which again reiterated that he took control of the city in 1351. The exact time frame of his domain over the city was retconned in Dark Ages Europe. In that source, the year that he replaced Valerianus as Prince was changed from 1351 to 1155.