Hendil is an Altmer citizen who can be found in Phaer on the island of Auridon. He can be found in Aninwe's barn trying to ease other Altmer afflicted with the same sickness as his son on mainland Auridon.
Hendil is the local alchemist living in Phaer, recently his son contracted a mysterious plague, and shortly afterwards it started to spread to the other villagers. According to Hendil, he and his assistant Amuur, work together to do what they can for the sick, using salloweed found nearby to create a salve to help stave off the disease in those who haven't caught it, and those who have.
The Vestige eventually gains access to the mine where the sickest people are kept there by Hendil and the mercenaries hired by him, to find that his son, Tancano, had been attacked and turned into a vampire. The "disease" was actually the people being turned into mindless thralls after being fed upon and the salloweed was used to help make people easier to feed to his son.
After killing his son, Hendil surrenders and the Vestige is given the choice of handing him over to the angry Velatosse (which will result in his death), or to the mercenary captain Netanwe (which will lead to his arrest).