(Supersister - Owed much to Caravan and Frank Zappa, though not in any particular order)
Had they decided to break up when their original lead singer left in 1969, we probably never would have had much of the Progressive Rock movement as we knew it in the 1970's. Supersister were a Dutch band (a country probably known more for Golden Earring and The Tee Set here in the States) who put Europe on the map as far as the Prog-rock movement was concerned.
Influenced a lot by the Canterbury scene in the UK in the mid-late 1960's with the likes of Caravan and Soft Machine, they were also very much influenced by early Mothers of Invention and the free Jazz and electronic music scene that was happening all over Europe from the 1950's onwards.
By today's standards, the band wasn't together all that long. Three albums worth before going separate ways in 1974, until a brief reunion in 2001 which sadly didn't become permanent owing to the loss of Sacha van Geest, one of the founding members to Cancer that year.
Still, Supersister have enjoyed a resurgence in popularity over the years because, like many of their counterparts from the period, it was never picked up by the mainstream and was deemed comfortably weird enough to remain timeless to those who never heard them in the first place.
Thank God for that.
Here is a cut off their second album "To The Highest Bidder", which was issued in the UK on Dandelion Records and came out in the U.S. for about a minute and a half. "A Girl Named You" starts off the original Side two.