Tilly

Tilly, Rowlf's mother, appeared on The Mike Douglas Show in 1966, during a week of Muppet co-hosting episodes. She appeared in the audience and didn't recognize her son (calling him "the funny looking dog" next to Mike Douglas). She was a redressed Rowlf puppet with a hat, shawl, eyelids and eyelashes. Rowlf writes a series of letters to his mother in a 1966 IBM meeting film. (YouTube)

According to Dog City, she taught Rowlf to let sweeping dogs lie.