Professor Hinkle is the sole antagonist of Frosty the Snowman. He is a magician hired to perform at the school's Christmas party. The narrator describes him as the worst magician in the world, as shown when his equipment falls and whose tricks go awry; he puts eggs into his magic hat, which all fall on the floor, and he fails to pull his mischievous pet rabbit, Hocus Pocus, out of the hat. He has a tendency to repeat adjectives and adverbs when excited or stressed, such as "Messy, messy, messy," or "Busy, busy, busy!"
After Hinkle's failed attempt at a magic show, the students to whom he was performing put Hinkle's magic hat on Frosty the Snowman, whom they had just created, and the hat brings the snowman to life. Seeing its magical properties, Hinkle takes the hat back along with the rabbit, hoping to become rich through use of the hat. However, Hocus escapes with the hat and takes it back to the children, who once again revive Frosty. When the children decide to send their friend to the North Pole by train so he can't melt, the Professor pursues them vowing to get the hat back.
Hinkle gets lost in the woods after a mishap on the train, but eventually catches up with Frosty and Karen, his friend who accompanied him on the trip up north. He ruins Karen's campfire and demands the hat back, only to watch the two run off so fast he couldn't catch them. However, he eventually catches up to them just as Frosty has brought Karen into a greenhouse and locks them inside, causing the snowman to melt. Fortunately, Santa Claus arrives and is able to magically revive Frosty, but is confronted by Hinkle, who once again demands the hat. However, Santa refuses to let him touch it, as it now belongs to the inanimate Frosty, and adds that Hinkle will receive no more Christmas gifts if he keeps on pursuing to get the hat. When Hinkle complains that even "evil magicians" need to make a living too, Santa softens a little and tells him that if he writes an apology to Frosty ("a hundred zillion times"), he might still receive a present of forgiveness. Realizing that this could mean a new magic hat he could actually use, Hinkle eagerly agrees, apologizes for all trouble he has caused, and runs off to get busy writing.
Hinkle appears during the end credits marching along with Frosty's friends, donning a brand new hat, which implies that he has already written up his apologies and Santa has kept his word. Hocus Pocus is also seen at his side, which implies the two have reconciled. Hinkle is last seen tipping his new hat as he and the others bid farewell to Frosty, who is leaving with Santa, promising to be back on Christmas Day.