The Wheelers are a race of disagreeable people who live in the Land of Ev.
The Wheelers have the forms of men except that they roll on all fours, their legs and arms being the same length. Instead of hands and feet they have wheels, which are made from the same material as finger-nails and toe-nails. The Wheelers wear gorgeously embroidered, tight-fitting garments.
They are harmless because they have no hands to punch or grab or scratch with, and no feet to kick with. They write warnings in the sand and act fiercely to make people afraid of them, in order to protect themselves. (Ozma of Oz)
In Dorothy Meets Ozma of Oz
The Wheelers chase Dorothy after she eats a lunch-box from the Lunch-box tree. They also chased Toto when he arrived, scaring him off in the direction of the Nome King. Ozma finally arrives, forcing the Wheelers to apologize to Dorothy and admit that they're not ferocious at all but must act that way because they only have wheels and no hands or feet. (Dorothy Meets Ozma of Oz)
In Return to Oz
The Land of Oz is overrun with Wheelers when Dorothy returns to Oz; everyone in the Emerald City is turned to stone so no one can resist them. They terrorize Dorothy and Billina until they find Tik-Tok and wind him up. Tik-Tok is then able to defend them. (Return to Oz)
In Lost in Oz
Alexandra Wilder and her party encounter a sign during their travels through Oz that reads "Beware the Wheelers". Later, they are attacked while camping during the night and are forced to fight off the Wheelers using a pistol. (Lost in Oz)