Abu Jafar Muhammad Ibn Muhammad Ibn al-Hasan Nasir al-Din al-Tusi is an Iranian Muslim, and was one of the greatest scientists, philosophers, mathematicians, astronomers, theologians and physicians of the 7th/13th century Islamic lands and he was also a prolific writer. He was born in Tus (Khurasan) in 597/1201 C.E. He learnt sciences and philosophy from Kamal al-Din Ibn Yunus and others. He died in Baghdad in 672/1274. His father was a jurist in the Twelfth Imam School. The school where al-Tusi was educated was mainly a religious establishment. However, while studying in Tus, he was taught other topics by his uncle, which had an important influence on his intellectual development. These topics included logic, physics and metaphysics. He also studied mathematics with other teachers, in particular algebra and geometry. His ability and talent in learning enabled him to master a number of disciplines in a relatively short period, and he showed a great interest for mathematics, astronomy and the intellectual sciences at a very young age. At the age of twenty-two or a while later, Tusi joined the court of Nasir al-Din Muhtashim, the Muslim governor of Quhistan, Northeast Iran, where he was accepted into the Islamic community as a novice (mustajib). A sign of close personal relationship with Muhtashim’s family is to be seen in the dedication of a number of his scholarly works such as Akhlaq-i Nasiri and Akhlaq-i Muhtashimi to Nasir al-Din himself and Risala-yi Mu‘iniyya to his son Mu‘in al-Din. In 1256 when the Mongols conquered Almut, Nasir al-Din joined Hulegu's service. Hulegu being himself interested in science, treated al-Tusi with great respect and he was deeply impressed by his knowledge, including his astrological competency; appointed him as one of his ministers, and, later on, as administrator of Auqaf. He was instrumental in the establishment and progress of the observatory at Maragha. He made significant contributions in a large number of subjects, and it is indeed difficult to present his work in a few words. He wrote one or several treatises on different sciences and subjects including those on geometry, algebra, arithmetic, trigonometry, medicine, metaphysics, logic, ethics and theology. In addition he wrote poetry in Persian. Being the chief scientist and the supervisor at the observatory established at Maragha, he made significant contributions to astronomy. The observatory was equipped with the best possible equipments, including those collected by the Mongol armies from Baghdad and other Islamic centers. The instruments included astrolabes, representations of constellations, epicycles, shapes of spheres, etc. He himself invented an instrument 'turquet' that contained two planes. After the devoted work of 12 years at the observatory and with the assistance of his group, he produced new astronomical tables called Al-Zij-Ilkhani dedicated to Ilkhan (Hulegu Khan). Although Tusi had contemplated completing the tables in 30 years, the time required for the completion of planetary cycles, but he had to complete them in 12 years on orders from Hulegu Khan. The tables were largely based on original observations, but also drew upon the then existing knowledge on the subject. The Zij-Ilkhani became the most popular tables among astronomers and remained so till the 15th century. Nasir al-Din pointed out several serious shortcomings in Ptolemy's astronomy and foreshadowed the later dissatisfaction with the system that culminated in the Copernican reforms. In mathematics, his major contribution would seem to be in trigonometry, which was compiled by him as a new subject in its own right for the first time. Also he developed the subject of spherical trigonometry, including six fundamental formulas for the solution of spherical right-angled triangles. In philosophy, his work on ethics entitled Akhlaq-i-Nasri became the most important book on the subject, and remained popular for centuries. His book Tajrid-al-'Aqaid was a major work on al-Kalam (Islamic Scholastic Philosophy) and enjoyed widespread popularity. Several commentaries were written on this book. In logic al-Tusi followed the teachings of ibn Sina (Avicenna). He wrote five works on the subject, the most important of which is one on inference. He wrote a famous work on minerals, which contains an interesting theory of colors based on mixtures of black and white, and included chapters on jewels and perfumes. He also wrote on medicine, but his medical works are among his least important. The list of his known treatises is exhaustive; Brockelmann lists 56 and Sarton 64. About one-fourth of these concern mathematics, another fourth astronomy, another fourth philosophy and religion, and the remainder other subjects. The books, though originally written in Arabic and Persian, were translated into Latin and other European languages in the Middle Ages and several of these have been printed. Tusi's influence has been significant in the development of science, notably in mathematics and astronomy. His books were widely consulted for centuries and he has been held in high repute for his rich contributions. Tusi’s fame in his own lifetime guaranteed the survival of almost all of his scholarly output.