* First ever appearance: The show premiered in 1989 with David Hasselhoff as Mitch Buchannon. So, technically, he was the first actor to appear on Baywatch.
* Longest-running cast member: Again, David Hasselhoff was the longest-running cast member, appearing in all eleven seasons.
* Other early cast members: Other notable actors who were part of the original cast include Pamela Anderson, Nicole Eggert, Gena Lee Nolin, Alexandra Paul, and Yasmine Bleeth.
So, depending on your criteria, the answer could be any of these!