Alaric is an inhabitant of the Refugee camp and essential for the Vampire quest line
Supply him with Blood
Alaric is weak because of starvation. He asks you for a drop of Blood or Bucket of blood. After delivering he will reward you with Sun cream for vampires as a reward. This can be shown to Horadric to make him believe you took care of the vampire and to end the vampire quest line.
He also points out to use the Witchers eye to find the vampires that turned him into one.