What role does Lord Ruthven play in The Vampyre?

Lord Ruthven epitomizes the outcast villain-hero of Gothic fiction: gaunt, pallid, and basilisk-eyed, he is devoid of compassion yet strangely attractive. Ruthven is, literally, a lady killer, and he especially relishes virgins. Apparently he does not suck men's blood and never directly threatens his younger friend, Aubrey; yet there is a characteristically vampiric exchange of energy between the two men. As Aubrey sickens with the realization of what Ruthven is, the vampire grows increasingly healthy, but once Aubrey recovers, Ruthven reverts to his former emaciated state. Before dying, Ruthven arranges with local robbers to have his corpse dragged to a nearby mountain where it will be "exposed to the first cold ray of the moon." The plot's weak link is Aubrey's refusal to save his sister from marrying a vampire by revealing Ruthven's identity despite his oath of silence.