My earliest drawings here show him as being a bit too Gandalf-ish, and more like a wizard than a professor. I like the guy on the far right a lot, but decided he looks too urban. He might be a great character for another story that takes place in a strange city, but doesn't seem like he would live in a forest.
Exploring further in another direction, this guy on the left is leaning too close to a Sigmund Freud-type....once again, might be good as a city-dwelling professor, but not someone close to the earth who talks to animals.
I continued playing with different outfits and hats, but still too much like "Gandalf in the City."
Upon further playing and sketching, and the advice of my friend Luke who suggested a "wool elbow patch sweater and hip waders, more like a biologist," I ended up with the guy on the bottom right, who seems to fit much better. I haven't done any final illustrations of the Professor just yet, only sketches, but when the time is right, he will be realized into fuller form for his "epic journey."