His close associates called him Herr Doktor, or Dr. LaVey, in the same manner that some musicians in the 1920's and 30's would be called "professor".
Using his full name, or Mr. LaVey is suitable.
"Consensus is the absence of leadership." Margaret Thatcher
"I'm fascinated with how primitive the human mind still is. It can be misdirected so easily." John Gaughan
"Success is uncommon. Therefore, not to be enjoyed by the common man." Cal Stoll