How many actors played Jason Voorhees?

Jason was portrayed by the following: Friday the 13th:
Ari Lehman (child)
Friday the 13th Part 2:
Warrington Gillette (unmasked) & Steve Daskewisz (masked) & Ellen Lutter (one scene)

Friday the 13th Part 3:
Richard Brooker

Friday the 13th: The Final Chapter:
Ted White

Friday the 13th: A New Beginning:
Tom Morga (hallucination)

Friday the 13th Part VI: Jason Lives:
C. J. Graham (most of the film) & Dan Bradley (Paintball sequence)

Friday the 13th Part VII: The New Blood to Jason X:
Kane Hodder

Friday the 13th Part VIII: Jason Takes Manhattan: Timothy Burr Mirkovich (child)

Freddy vs. Jason:
Ken Kirzinger & Spencer Stump (child) Francisco