Final answer:
The Kinks, an early British hard rock band, were renowned for their song 'You Really Got Me' with a repetitive guitar/bass riff, significantly influencing the hard rock genre.
Step-by-step explanation:
The early British hard rock band known for writing many songs with a repetitive guitar/bass riff, including their biggest hit 'You Really Got Me,' is The Kinks. This band was part of the British Invasion of the 1960s and significantly influenced the birth of hard rock and heavy metal genres. The Kinks' use of power chords in 'You Really Got Me' particularly set a precedent for many subsequent rock bands, highlighting a key element in the genre's development.