From Muppet Wiki

The Scarecrow is one of Dorothy Gale's companions on the way to the Emerald City in The Muppets' Wizard of Oz. Rescued from a field where he was tormented by crows, the strawman, or straw-frog, joins Dorothy, in the hopes of acquiring a brain. Glinda appears to be smitten with him.

The Scarecrow puppet is differentiated from the regular Kermit puppet in that it is made from green burlap instead of felt.

When the Muppets performed a Wizard of Oz number in The Muppets Go to the Movies, the Scarecrow character was played by Scooter.