Walter Leddy is a boy who attended P.S. 38 around the same time as Edna Birkdale. At one point, Birkdale drew a comic of him dipping Martha's braid in his inkwell. He is a scoundrel, according to Edna.
The comic helped Nate and his scavenger hunt team (Nate's Non-Stoppers) Find one of the items on the list.
Which was also their first item. The desk with the ink well was found by Breckenridge Puffington III in Mrs.Clarke's classroom
Walter may be Edna Birkdale's enemy. One of his actions was notable enough for her to draw him out of disgust.