They were always going to be on the list somewhere. People get a bit tired of perpetual Beatles mentions, and in the process forget just how much they changed music. While their early hits single-handedly invented Pop (a genre that, for all intents and purposes, can be considered Rock n Roll / RnB 'lite'), their later stuff helped define other sub-genres of Rock - from their psychedelic phase helping shape the sound of the 60s, to their heavier songs from the White Album helping pave the way for Hard Rock and Metal sub-genres.
When one learns the guitar, there are a few acts towards which one aspires. Eric Clapton, Jimmy Page, Angus Young... but one figure overshadows them all. Possibly the most dedicated guitarist ever, who could coax sounds out of his instrument the likes of which haven't been heard before or since, and who was at one point caught sleeping next to his guitar while in the US Army: Jimi Hendrix. The star by which practically all contemporary rock, blues and RnB guitarists steer by. His sound is truly amazing, his talent unmatched.
The wildcard on the list. Beginning life as a fairly conventional 60s pop group (inspired heavily by psychedelica), before moving towards progressive rock, Pink Floyd broke through the haze that ensnared similar acts such as Hawkwind and Genesis and went on to become true musical giants. Their sound, driven by the rhythm section's slow but driving pace, soaring guitar solos and lyrics on complex themes, weathered the fads and trends of the industry with grace. While genres rose and fell, Pink Floyd's songs remained the same.
With the Zep, rock music got a darker and heavier. Without them, Hard Rock and Heavy Metal probably wouldn't have existed, although as we mentioned earlier the precedents for both these genres sound occurred in earlier Beatles songs such as Helter Skelter. But the Zep took it to a new level, with wild, fast, brutal songs like Communication Breakdown on their first album. Throughout all their music was an undercurrent of mysticism, which both genres adopted in the form of magical, infernal, otherworldy imagery.
This was the man who wrested RnB and Electric Blues into a thing called Rock and Roll. As John Lennon famously said, "if Rock and Roll was called anything else, it'd probably be called Chuck Berry". While its hard to assign one individual with single-handedly creating a genre, in this case its probably valid: of all music contemporary to him, he has the sound we would recognise as truly 'rocky'. This innovation, combined with his marketing to a teenage audience, helped thrust Rock and Roll forwards towards the worldwide popularity it enjoys today.