Al-Tusi, also known as Nasir al-Din al-Tusi, was a prominent Persian polymath who lived during the 13th century. He made significant contributions to various fields, including astronomy, mathematics, and philosophy. Al-Tusi is best known for his work in developing trigonometry and for his influential astronomical model, which improved upon the Ptolemaic system. In addition to his scientific achievements, Al-Tusi founded the Maragha Observatory in present-day Iran, which became a center for astronomical research. His writings, particularly the Tusi-couple, played a crucial role in the transition from medieval to modern astronomy, influencing later scientists like Copernicus.