He was an immortality quester, and created the "From Hell" letter (of Jack the Ripper's), he was a sorcerer and created the portal in the letter as well. He appears in Broken.
Hull accidentally wound up inside his portal for many years until he was released by Elena's blood touching the "From Hell" letter. Despite his bewilderment of finding himself in a different time and place, he eavesdropped on Elena and her companions, learning not only was she a female werewolf but she was pregnant with twins.
He became determined to seize Elena's children to use as a means of obtaining wealth and perhaps dissect them to uncover a clue in his quest for immortality.
He almost killed Zoe Takano (who just barely survived thanks to her vampiric regenerating powers) but was eventually killed by Elena who tore his throat out (while still in human form) out of desperation to protect her unborn children.