From an interview with Lawrence French on Facebook, 9/23/13:
LAWRENCE FRENCH: As Lord Summerisle, you have a rather distinctive hairstyle in the film.
CHRISTOPHER LEE: Yes, but it's not my hair, I'm afraid. It's supposed to represent the rays of the sun, that golden-blonde, leonine wig. It comes from the emblem of Summerisle. It's all very symbolic, representing Nuada, their God of the Sun. But quite obviously it's not my own hair. My own hair is what you see here, and that was obviously a wig.
His appearance in the movie as Teaser is exactly as it is described in the book, long black hair and a shoddy dress.
His grandfather, "a distinguished Victorian scientist, agronomist, freethinker", bought the island in 1868.
His last name is Morrison! (pg 70 of the novel.)