Mary Pop ‧ pins /ˌme ə ri ˈpɒpənz $ -ˈpɑː-/ BrE AmE
someone whose behaviour is almost too good to be true is sometimes compared to Mary Poppins, the main character of a 1964 US film in which Julie Andrews appears as a ↑ nanny (=a woman who is employed to take care of the children in a family) called Mary Poppins, who has magical powers and can fly