Omar, Khayyam, Sadi, and Saadi are all Persian poets. Omar was a Persian poet of the 8th century who wrote in Arabic and is best known for his collection of poems called Diwan. Khayyam was a Persian poet, mathematician, and astronomer of the 11th century who wrote in Persian and is best known for his collection of poems called Rubaiyat. Sadi was a Persian poet of the 13th century who wrote in Persian and is best known for his collection of poems called Bustan. Saadi was a Persian poet of the 13th century who wrote in Persian and is best known for his collection of poems called Gulistan. Omarkhayyam is a combination of the names of Omar and Khayyam, two of the most famous Persian poets.