Complex sentence: Majid M. Naini is a leading scholar of Rumi, the 13th century Persian mystic (Sufi), who has been the best-selling poet in the U.S. for the past several years.
Split into simpler sentences: Majid M. Naini is a leading scholar of Rumi, the 13th century Persian mystic (Sufi). Rumi has been the best-selling poet in the U.S. for the past several years.