Professor Thistlethorpe first appears as a caterpillar. However, he has six arms and four legs (for a total of ten limbs), even though real caterpillars, like all insects, only have six limbs.
He has green skin, dappled with orange and darker-green spots. His face is a lighter shade of green than the rest of his body, with a long, vertical orange stripe in the center of his face that resembles a nose.
He wears glasses with square lenses, and he has insect-like mouth parts flanking his otherwise human-like mouth. His lips are orange.
During the events of See Mr. Peanutbutter Run, Professor Thistlethorpe encases himself in a chrysalis to undergo metamorphosis into a butterfly.
His butterfly form has two pairs of orange wings with purple and red-orange spots. His butterfly form appears nearly-identical to his caterpillar form, aside from the addition of wings.
He can later be seen flying through the skies in his butterfly form after Mr. Peanutbutter's ski race against Woodchuck-Coodchuck Berkowitz.
Thistlethorpe seems to be a wise caterpillar who has a deep love for the philosophy behind skiing. Little else is known about him. He becomes a mentor to Mr. Peanutbutter in See Mr. Peanutbutter Run.
When he first meets Mr. Peanutbutter. he declares Mr. Peanutbutter disgusts him, yet at the same time he sees potential in him.
He then tells Mr. Peanutbutter to meet him at the summit at daybreak. The scene then cuts to the two of them at the top of the summit.
He then tells Mr. Peanutbutter to break his skis in half to which Mr. Peanutbutter replies he didn't bring them. The professor then asks Mr. Peanutbutter to read a book of poetry.
Later, when questioned by the professor about reading the book of poetry, Mr. Peanutbutter says he forgot to. The professor tells him that is excellent as skiing is not about reading books and he has passed the test.
He tells him skiing is about speaking truth to power. He then congratulates Mr. Peanutbutter on speaking this eloquently and that he is the finest student he has ever taught and that he loves Mr. Peanutbutter.
He allows Mr. Peanutbutter to graduate from the academy the next day.
Mr. Peanutbutter arrives back in the classroom the next day to pick up his diploma only to discover Thistlethorpe is now encased in chrysalis form to become a butterfly. He asks for some final advice about skiing.
Thislethorpe is about to tell Mr. Peanutbutter to keep his legs bent while skiing, but his head is fully encased before he can finish his sentence.
He makes a cameo appearance at Mr. Peanutbutter's housewarming party in The Dog Days Are Over.
- He seems to have remained good friends with Mr. Peanutbutter, even after Mr. Peanutbutter graduates from ski school.