Off the top of my head, John Sajo. He had been growing cannabis covertly for 30 years, and his product made all other growers take notice.
I think what made his mentorship effective was:
o- He had me doing the process, not just showing me.
o- He told me what he knew, what he didn't know, what he suspected, and what others suspected
o- I was encouraged me to experiment
o- I was given the minimal amount of what was necessary for near 100% success
o- The clones for my first garden came directly from Ed Rosenthal (again, setting me up for success)
o- We had fun the whole time I was learning