Complex sentence: During this time he had a relationship with Etta James before she achieved her fame as a blues singer and recorded a few 45 rpm records himself, the best known of which was called "You Got the Nerve of a Brass Monkey".
Split into simpler sentences: During this time he had a relationship with Etta James before she achieved her fame as a blues singer and recorded a few 45 rpm records himself. His most successful record from this time was titled "You Got the Nerve of a Brass Monkey".