The band originated in Toronto in 1968 with three members: Alex Lifeson, bassist and front man Jeff Jones and drummer John Rutsey. Very shortly, Jones was replaced with a new bassist and vocalist, Geddy Lee. The three-man band did some recording and managed to get a small following that led to a debut album in 1974. Rutsey had developed diabetes and left the band out of health concerns. He was replaced by Neal Peart and that configuration - Lifeson, Lee, and Peart, has been Rush ever since.
While Rush's initial recordings were fairly mainstream rock and roll, they were heavily influenced by some of the early 70s prog giants like King Crimson and Yes. Rush had a rather unique compositional style. Lee and Lifeson were principally concerned with instrumental arrangements and Peart seemed to be more focused on the lyrics. Both elements were highly progressive. The instrumentals were increasingly complex and sophisticated while Peart tended to write in sweeping lyrical themes influenced by his love of science fiction and fantasy literature.
Main Creative Force
Because all three contribute somewhat equally to the mix, it is very hard to single out one person as a main creative force. I think for many people, however, Peart is the driving force behind what makes Rush sound like Rush in that his lyrics often form epic tales of the fantastic. That element really seems to permeate their music and serves as something of a signature.
Most Likely To Be A Mainstream Rocker
All three members of the band are prefectly capable of being mainstream rockers. Of the three, Lifeson seems to be the one lest dedicated to the complexity and fantastic nature of their music. He was the orignal founder and in their earliest days, there was little prog influence visible. Consequently, he would be my guess as the one best suited to mainstream rock. It is hard to imagine Geddy Lee or Neal Peart ever being comfortable doing Bruce Springsteen songs, but you can kind of see Lifeson dabbling in everything.
First Hint of Prog Brilliance
In the mid 70's, the band really transformed from a hard rock band to a true progressive giant and the clearest indication that they'd gone that way seems to me to be the 1978 album, 'Hemispheres'. The album incorporates more synthesizer than anything previous and has rather extensive and exotic percussion in use, as well. The album consists of four pieces, one of which 'La Villa Strangiato' is actually subtitled 'An Exercise in Self-Indulgence'. This album really established the direction Rush would be going for the remainder of their careers.
Released in 1981, 'Moving Pictures' is probably regarded by most fans as the pinnacle of Rush's music. Their most recognizable tune, 'Tom Sawyer' opens the album and has been a staple of live shows for over thirty years. The album, which is undeniably progressive rock, reached number 3 on the Billboard chart which gives some indication of how pervasive Rush's popularity has been outside the narrow niche of prog. They have millions of fans who would prefer to think of themselves as heavy metal or hard rock fans, as well as plenty of prog fans behind them. This album is also on a lot of greatest albums lists.
Influenced By Them
Since the seventies, bands with progressive styles tend to be more of an amalgam of hard rock, metal, and symphonic sounds. Rush was very much the pioneer of blending all these elements into a seamless and extremely popular sound. Virtually any band with progressive aspects that has emerged since the early 80s has probably been influenced by Rush.
Rush consists of three extremely talented musicians and their musical styles, while extremely progressive at times, make it clear they can jam with the heaviest metal or hardest rock. They are one of the most successful artists on this list having sold an estimated 40 million units worldwide. Most aficianados of popular music rank all three musicians as among the best in their instrument and Peart, in particular, is regarded as one of the very best rock drummers. Critics divide on Rush precisely at the taste line on prog rock. Some consider Peart's lyrics to be brilliant while others consider him pretentious. The same is generally said about Rush's instrumentals which are simultaneously described as "brilliant" and "needlessly complex". They have become something of a poster child to the almighty RRHOF's disdain for Prog. About 80% of the Hall's inductees have sold fewer albums and influenced fewer bands and sold out fewer concerts. Yet the Hall continued to staunchly ignore Rush until 2013 when they were finally inducted. In career album sales by a Canadian artist, Rush is probably only second to Neil Young who has been inducted twice. Their invisibility to the Hall was a scathing indictment to the hypocrisy and unfettered bias that ruled its induction process. The times, they are a changin'.
My Personal Take
I have classified Rush as commercial prog because with their success both in sales and in album rankings, it is impossible not to describe them that way. At the same time, Rush is several different bands in different eras. In the mid-late 70s, they were very progressive and need to be placed alongside ELP and Yes for the sheer complexity and musicianship, but they were always a harder rock band than either of those and gravitated a bit more toward the metal label applied to Led Zeppelin and others. When you look at later bands, Dream Theater is in many ways, the most Rush-like. Rush as a band has both the sales, the reputation, and the influence to be placed alongside Zeppelin or Pink Floyd among the ranks of somewhat-progressive bands yet they continued to be ignored for far too long.