Complex sentence: Mardin began his career at Atlantic Records in 1963 as an assistant to fellow Turkish emigré Nesuhi Ertegün, the brother of the company's co-founder and a legendary jazz enthusiast, whom he met at the Newport Jazz Festival.
Split into simpler sentences: Mardin began his career at Atlantic Records in 1963 as an assistant to Nesuhi Ertegün. A fellow Turkish emigré, Nesuhi was the brother of Ahmet Ertegün, Atlantic's co-founder and a jazz enthusiast when they met at the Newport Jazz Festival.