Hindaril is an Altmer warrior and powerful vampire located within Redwater Slough. According to Melisande he was so powerful that he was sealed within Redwater Slough to prevent him from terrorizing Cyrodill.
"You have come across a vampire or two in your travels, perhaps? I assure you, they are nothing like what you must face. The vampire you seek is powerful, so powerful that those who sought to destroy him were unsuccessful, no matter what they tried. The best they could do to was to imprison him underground, where he survives to this day." -Melisande