The Clown is the country bumpkin son of the Old Shepherd. He’s not very bright (he’s easily duped by Autolycus, who picks the Clown’s pockets and later scams him and his father into thinking he’s a nobleman). Overall, the Clown’s job is to help inject a bit of levity (by way of his dim-witted antics) into the play, which is what Shakespeare’s “rustic” clown figures tend to do. (Compare him, for example, to the Dromio twins in The Comedy of Errors and Grumio in The Taming of the Shrew.)
While the Clown doesn’t have much going on in the brains department, he is a bit of a player. During the sheep-shearing shindig in Act 4, we find out that he’s got a little somethin’ somethin’ goin’ on with Mopsa and Dorcas, which makes for some good entertainment when the two country bumpkin-ettes come face to face at the festival and make some catty remarks to one another.