Wendy is a given name generally given to girls in English-speaking countries. In Britain during the English Civil War in the mid-1600s, a male Captain Wendy Oxford was identified by the Leveller John Lilburne as a spy reporting on his activities. It was also used as a surname in Britain from at least the 17th century. Its popularity in Britain as a feminine name is owed to the character Wendy Darling from the 1904 play Peter Pan and its 1911 novelisation Peter and Wendy, both by J. M. Barrie. Its popularity reached a peak in the 1960s, and subsequently declined.
https://en.wikipedia.org/wiki/Wendy