Marguerite (Margot) Ruddock (1907-1951), who used the stage name Margot Collis, was an actress, poet and singer. She had a relationship with W. B. Yeats starting in 1934. Their correspondence was published as Ah, Sweet Dancer (1970).
Yeats edited her poems for publication, but it is not clear how much change he made to them. He included some of them in the Oxford Book of Modern Verse, which he edited.
She was married twice: first to John Collis, with whom she had a son, Michael, and secondly to Raymond Lovell, with whom she had a daughter, Simone Lovell. She died in 1951, when she was just 44.
During her marriage to Raymond Lovell she had an affair with Yeats. She loved him dearly while he was merely getting one over on Maude, his true love, by being promiscious at an older age; something that he hadn't done when he was a younger man. The affair broke down and Margot Ruddock became mentally unstable, something that Yeats links to in his poem "A Crazed Girl".