Late Roman Empire
Thaddeus is a Nosferatu methuselah, embraced while the Roman Empire still existed. Haunted by the idea that the old Roman gods had forsaken him, for refusing to come to them (i.e. dying), Thaddeus indulges in the practice of cattle sacrificing as a way to appease his gods.
Besides his fear of displeasing the old gods of his youth, Thaddeus is also very careful regarding the preservation of his unlife and of the vampire race as a whole. That led him to believe the serum that was once being developed by Louis Pasteur, then a vampire under the guise of Jacob Prestor, as a way to cure vampirism was a menace that could led all vampires to destruction. This line of thought led Thaddeus to fool and manipulate the Prince of Denver, Edward Williams to order the death of Prestor/Pasteur. After accomplishing his plot, Thaddeus left Denver for unknown whereabouts.