The Wonder Who? was a nom de disque of The Four Seasons for four single records released from 1965 to 1967. It was one of a handful of "names" used by the group at that time, including Frankie Valli (as a "solo" artist even though the Four Seasons were present on the record) and The Valli Boys. Wonder Who? recordings generally feature the falsetto singing by Valli, but with a softer falsetto than on "typical" Four Seasons recordings. (More from Wikipedia)
Masquerading as the Wonder Who? – at the same time that the Who and the Guess Who were current – the Four Seasons released a version of "Don't Think Twice, It's All Right" with Frankie Valli singing an exaggerated falsetto. And there is the excellent cover by the Jimi Hendrix Experience of "All Along the Watchtower", which seems to be on everyone's short list of the greatest Bob Dylan covers of all time.