Zinna, the evil with from the east of Oz, had created a race of living scarecrows. They were her former enemies and the transformation to scarecrows included removing their brains. Bartleby had been Zinna's unwitting pawn and thus she didn't remove his brain.
Like most characters of the Grimm Fairy Tales lore, Scarecrow has her inspiration in fairy tales or literature. Scarecrow is inspired on the Scarecrow from L. Frank Baum's children's book The Wonderful Wizard of Oz (1900).
Major Story Arcs
Grimm Fairy Tales Presents Oz
After Zinna's death (killed by Dorothy), townspeople hung Scarecrow on a pole and threatened to burn him alive. He was rescued by Glinda after he shouted he knew the location of Grafft, a wizard Glinda needed to complete the Veridian Scepter.
Oz: Age of Darkness
Seventyfive years have passed. Dorothy Gale is now queen of Oz, ruling with Thorne, Scarecrow and Toto by her side. The Dark Queen recovers the Warlord of Oz and sets him loose on Oz. He manages to kill Thorne, Scarecrow and Toto before beheading Dorothy Gale. He then sits on the throne of Oz himself.