Charles Hamilton (also known as Professor Hamilton, the Professor, and Prof.) was a historical scholar and once a professor at Oxford, and was (prior to the beginning of the series) inducted into the organization known as The Circle Of Knights. On their orders, he moved to the United States—specifically to Castlewood, West Virginia, in order to seek out the heir of King Arthur. There, he became a history teacher at Billy Bannister's school. He first got to know Billy after an accident involving the flooding of a bathroom. Once the Bannisters lost their house, Mr. Hamilton volunteered to be the tutor of Billy, Bonnie Silver, and Walter Foley. As their adventures went on, he revealed his knowledge repeatedly and became a trusted advisor and beloved companion to those around him.
Professor Hamilton was the husband of Dorcas Hamilton and father to at least one daughter, Elizabeth. On the night of Elizabeth's marriage, Dorcas became deathly ill with a case of food poisoning and was hospitalized. She died that night, leaving Charles distraught. It is later found that Dorcas' food poisoning was due to a scheme by Morgan Le Fay.
It is also later found (and proved through the Professor's ability to use Excalibur) that Professor Hamilton is a direct descendant of Merlin, who was King Arthur's advisor and a prophet. He is permanently transluminated at the end of Tears of a Dragon. In the final chapters of The Bones of Makaidos, he returns form Heaven to officiate Billy and Bonnie's wedding, and they named their son after him.