They were not solely responsible for devising folk-rock, but they were certainly more responsible than any other single act (Dylan included) for melding the innovations and energy of the British Invasion with the best lyrical and musical elements of contemporary folk music.
Although they only attained the huge success of the Beatles, Rolling Stones, and the Beach Boys for a short time in the mid-'60s, time has judged the Byrds to be nearly as influential as those groups in the long run.