Complex sentence: Robert Bly (born December 23,1926) is an American poet, author, activist and leader of the mythopoetic men's movement, most famous for his' (1990), which spent 62 weeks on the The New York Times Best Seller list.
Split into simpler sentences: Robert Bly (born December 23,1926) is an American poet, author, activist and leader of the mythopoetic men's movement. His most commercially successful book to date was' (1990), a key text of the mythopoetic men's movement, which spent 62 weeks on the The New York Times Best Seller list.