Rock lead guitar developed from country and blues, with a bit of jazz thrown in. But in the mid to late '60s, it became a unique entity, while still showing its roots.
The early practitioners of rock soloing were often guilty of overreaching: wide quivering vibrato, too many purposeless notes, and lack of a 'story', an arc from beginning to end. Am I being too intellectual about rock? Hell no. Robert Johnson's lead playing told a story, and was integral to the song, and the best country and jazz players understood that concept too. And some of the early primitive rockers told great instrumental stories, like Chuck Berry.
Rock soloing became an art, and guitar heroes with distinctive styles started to appear. One of the earliest was John Cipollina of Quicksilver Messenger Service.
Cipollina had a unique guitar sound, mixing solid state and valve amplifiers as early as 1965. He is considered one of the fathers of the San Francisco psychedelic sound. He played with finger picks, thumb picks, and used a whammy bar extensively which, he explained to Jerry Garcia, was to make up for his weak left (tremolo) hand. Even more unusually, he attached six wurlitzer horns to the top of his distinctive amplifier stack. His style was highly melodic and expressive. Cipollina's classical past no doubt influenced his guitar style, which was miles beyond the usual blues-scale, pentatonic work of many of the other psychedelic-era guitarists. His work on fellow dueling guitarist Gary Duncan's electric arrangement/adaption of Dave Brubeck's "Take Five", retitled "Gold and Silver," which appears on the eponymous first album of Quicksilver, is an excellent example of how Cipollina took rock to places it usually didn't dare to venture.
Here's the website his family keeps for him:
John Cipollina's guitar sounded like no other. His unique resonance touched people in places they didn't know existed. His signature sound will stand alone for all time as a part of the musical thread the San Francisco Bay Area has wrapped around the world.
There are some great audio & video clips here.
Here's a clip of Quicksilver, and John soloing on his trademark Bigsby-equipped Gibson SG:
Here are two from his site, short clips:
Update: Videos changed because somehow YouTube swallowed and ate the originals. We'll see how long these last, dammit. And IMHO, when Dino Valente re-joined the band, it was their downfall into lounge-pop hackery. Like when Phil Collins took the reins of Genesis from Peter Gabriel and turned them into a finger-poppin' Vegas act.