Lennon and Dylan took rock-r-roll away from the cars-n-girls stuff and into more serious lyrical territory. 'Rock' is serious bidness, but I love the carefree fun of 'rock-n-roll'. To me, 'Masters of War' or 'Being for the Benefit of Mr. Kite' have nothing to do with rock-n-roll. 'Johnny B. Goode' has everything to do with rock-n-roll.
Well I guess if you phrase the question as 'most important in rock' rather than 'rock-n-roll' then Lennon or Dylan are the right choices. They turned rock-n-roll into simply rock.