I'd have to say Roy too, and give an honourable mention to Kenny. Ken, though not as prolific as Roy or Don, was certainly an old-time herper and I definitely appreciate his contribution to the hobby. What can I say about Roy? Well, everyone knows his tagline: "celebrating 25 years of herp breeding" so he's certainly been around for a while. Roy is definitely a pioneer in this hobby and is a hell of a good guy (on the boards and in person).
I don't know enough about Don to say anything meaningful.