A band known as the Paramounts was led by Gary Brooker and Robin Trower back in 1964 but the band fell apart two years later. Brooker later formed a new band in 1967 known as Procul Harum. The name, was actually taken from a cat owned by a friend. The cat's pedigree name was Procul Harum including the breeder's prefix - Procul.
Brooker and Trower were, like many young British musicians, heavily influenced by American pop music from the fifties. The Paramounts built their limited success off Lieber and Stoller hits, initially. Musically, as PH grew in popularity, they proved to be very eclectic. Their musical style had obvious classical overtones but also carried rock and jazz elements.
Main Creative Force
From the very beginning, Gary Brooker has been the leader of PH, however it is Keith Reid who might be their primary creative force. Reid has always been the prinicpal songwriter who embodied the romantic and mystical elements of their music.
Most Likely To Be A Mainstream Rocker
Robin Trower, who was in and out of the group over the years, has had a successful mainstream rock and roll career so he really has to be the winner on this topic. Trower, while not exactly a household name in the US, is known as a superb rock guitarist and has even recorded several power-trio albums with former Cream bassist, Jack Bruce. That basically puts Trower in the same general atmosphere as Eric Clapton which should be sufficient to make this point.
First Hint of Prog Brilliance
Their very first album, 'Procul Harum' produced their biggest hit,'A Whiter Shade of Pale' was a very obvious statement of the style of music the band could produce. The song, while not extraordinary from a melodic and instrumental standpoint, had amazingly complex and mystifying lyrics by Reid which really formed the basis of the band's progressive legacy. Other hits like 'Conquistador' were equally average from an instrumental standpoint but impressive lyrically.
For a band with few actual pinnacles, this is probably the closest thing you can find. In truth, Procul Harum was not a giant in the music business, but some of their early songs have lived on for forty years first with AOR format stations and now with classic rock format.
Influenced By Them
It's really hard to find any clear influence of Procul Harum's music on others. There are a lot of references to them in movies and literature from the past thirty years or so, however. The song 'Whiter Shade of Pale' shows up being played by a church organist in 'The Commitments' and Douglas Adams titled a book after the PH album, 'Grand Hotel'.
The band has been an on and off experience over the years with Brooker and Reid being the constants among a wide array of supporting musicians. Their discography includes eleven albums and all have enjoyed reasonable success though none were considered chart-busters. The band still performs, usually in tandem with other prog icons like Yes and Jethro Tull. Oddly, they are hugely popular in Scandinavia, moreso than anywhere else in the world.
My Personal Take
I liked everything I ever heard by Procul Harum, but I never invested in their records until recently. The US version of their first eponymous album is outstanding, as is the later 'Grand Hotel' but for my money, they never turned out a bad record.