In fact, he was the last survivor of a species that battled the Utluntu, a truly vampiric race. They tricked the Utluntu into trapping themselves in pocket universes. He trapped himself and Lilu, the last Utluntu, intending to be imprisoned together for all time.
However, over the centuries, Nepesht forgot his mission and identity, and escaped to Earth in 2565. This allowed Lilu to escape as well. After Bernice Summerfield helped him recover his memory in 2579, he once again trapped himself and Lilu in a pocket universe. (PROSE: Possum Kingdom)