Who was the celebrity in the center square on the first airing of Hollywood Squares in the 1960s?

My guess is:

Paul Lynde was the center square on the Hollywood Squares for most of it's run.

from http://www.chris-lambert.com/RULES/HollSquares.html

"Paul Lynde was, of course, the 'center square' more often than any other human, but he didn't appear on either the first or last episodes. The
very first 'center square' in 1966 was Ernest Borgnine; the last on NBC, Wayland Flowers & Madame. Paul left the show before its NBC run ended, but returned for part of the final syndicated season."

Kelley's the Girl !
"Ernest Borgnine was the first center square when the show premiered on NBC on October 17, 1966. Paul Lynde appeared the second week but didn't appear in his permanent center square position until the fall of 1968." - The Internet Movie Data Base

More on The Hollywood Squares here.

Great question and great answer!