Rakagore

Rakagore is known to have lived for as long as the Roman Empire, where he was worshiped by the Romans. In the 90's he holds his lair in a mental institution where he's posing as a doctor and feeding of the sick. When he holds a ritua in the basement, to make 6 brides sacrifice their souls so that he may walk the earth and have his "Dark age" for a hundred thousand years, Buffy shows up and slays him.