Supertramp was originally formed in 1969 by Rick Davies and Roger Hodgson. The first incarnation of the band was called Daddy but was renamed in early 1970. Their music has always carried a certain amount of progressive styling due to the keyboards and Hodgson's unique voice, but they were a fairly successful mainstream pop-rock band in the late 70s with the rise of the AOR radio format.
Davies was primarily a jazz and blues influenced musician while Hodgson was much more pop-oriented. He was a fan of the growing psychedelic movement in Britain when the two got together and formed Supertramp. Despite their disparate influences, the two of them worked well together and collaborated very effectively as composers. Guitarist Richard Palmer became the lyricist for Davies and Hodgson's tunes in the early days.
Main Creative Force
Between Davies and Hodgson, it is difficult to identify the more influential of the two. But Davies probably gets the nod. He really lent more to the direction of the band and the arrangments than anyone else and was generally the most significant creative force
Most Likely To Be A Mainstream Rocker
Davies' work as a keyboardist with Supertramp was probably the most versatile instrumental work in the band and would have been the most likely to translate to other styles of music. His electric piano work is clearly jazz-influenced but could easily be worked into any popular artist of the day.
First Hint of Prog Brilliance
The band's breakthrough, commercially, was probably the album 'Crime of the Century' which came out in 1974. It included the radio hits 'Dreamer' and 'Bloody Well Right'. Both songs were unique and critically acclaimed as well as being big sellers. In a lot of ways, Supertramp was showing signs of a band that could successfully bridge the gap between pop and prog rock.
Since Supertramp was a popularly successful prog-ish group, it's most successful album, Breakfast in America, really has to be considered it's pinnacle. The album came out in March, 1979 and spawned a number of radio hits including 'The Logical Song', 'Breakfast in America', 'Goodbye, Stranger', and 'Take the Long Way Home'. It was huge in the US and France and slightly less so in their home country of England. It went quadruple platinum, won two Grammys, and spent six weeks at number 1 on the Billboard album chart.
Influenced By Them
Supertramp was really more of an arena rock band with some original and unique elements and as such, they were probably influential on the first generation of MTV arena stars. In some ways, their vocal styles and hooks previewed the hair metal bands that would flood the LA clubs in the 80s.
Tramp really peaked with 'Breakfast in America' and subsequent albums suffered from increasing strife between Davies and Hodgson. Hodson left the band in 1983 and Davies soldiered on, taking over the lead vocal duties and continuing to create new music for Supertramp. But the collaboration of the two really defines the Supertramp sound and sadly, we're never going to hear that again.
My Personal Take
Supertramp was always a band that was kind of sitting right on the border between commercial popularity and progressive styles. They weren't quite mainstream but were close enough to it to sell tons of records and get tons of radio airplay. In an earlier day, they probably wouldn't have managed to get on the air but in the early days of AOR radio, they were huge. I remember from my college days that KY102, the main album-rock station in Kansas City, played Tramp all the time. I liked them but wasn't a huge fan.