Wikipedia
Gwendolen is a feminine given name, in general use only since the 19th century.
It has come to be the standard English form of Latin Guendoloena, which was first used by Geoffrey of Monmouth as the name of a legendary British queen in his History of the Kings of Britain . He reused the name in his Life of Merlin (c. 1150) for a different character, the wife of the titular magician " Merlinus", a counsellor to King Arthur; the metre shows that Geoffrey pronounced it as a pentasyllable, Guĕndŏlŏēnă, with the "gu" pronounced . Dr. Arthur Hutson suggests that "Guendoloena" arose from a misreading of the old Welsh masculine name Guendoleu; Geoffrey may have mistaken the final U for an N, then Latinized *Guendolen as a feminine name to arrive at Guendoloena. In the Vita Merlini, however, Geoffrey Latinizes the masculine name of Gwenddoleu ap Ceidio as Guennolous. Spelled Gwendoloena, the name reoccurs in the anonymous Latin romance De Ortu Waluuanii belonging to Arthur's queen Guinevere.
It did not become a common English given name until the 19th century. Gwendoline was in use in England by the 1860s (an early example being Lady Gwendoline Anson, born c. 1837, a daughter of the 1st Earl of Lichfield), and Gwendolen appeared in Daniel Deronda, written by George Eliot and published in serialized form 1874–6.
Gwendolen (United Kingdom title) a 1989 novel by Nigerian-born writer Buchi Emecheta, also known by its United States title The Family. It is her tenth novel.