John Stamos as Zack
The ever so talented and insanely attractive John Stamos had an appearance as Zack on Season 9, Episode 22 “The One With The Donor”. Monica and Chandler talk to a doctor after doing some fertility testing and are are told to consider a sperm donor. Chandler thinks of a coworker who may be perfect. Unbeknownst to Zack, played by John Stamos, Chandler invites him over as a potential candidate.