From creator Sherwood Schwartz' "bible" of the characters:
"The Unofficial Gilligan's Island Handbook"
"While the Professor might not have a poetic personality,
he always seems to have the most sensible solutions.
He's actually the only level-headed person on the island,
a bookworm who rarely displays his emotions - in short,
a shipwrecked Spock. He is clearly the castaways'
guiding light and silent leader. He prefers to sit quietly
in the background and let the others think the Skipper
runs the island. But when it comes to judicial affairs,
life-threatening matters, or possible rescue attempts,
the Professor unobtrusively assumes leadership."