One of the greatest scientists, mathematicians, astronomers, philosophers, theologians and physicians of the Middle Ages. Al-Tusi was a prolific writer who wrote many treatises on varied subjects such as Algebra, Arithmetic, Trigonometry, Geometry, Logic, Metaphysics, Medicine, Ethics, and Theology. Even now some of his works are standard textbooks in Iran. Al-Tusi was kidnapped by the Isma'ili Hasan Bin Sabah's agents and sent to Alamut where he remained until its capture by the Mongol Halaku Khan in 1256. Impressed by Al-Tusi's exceptional abilities Halaku Khan appointed him as one of his ministers. Later, he served as an administrator of Auqaf. Al-Tusi built an observatory, containing a twelve-feet wall quadrant made from copper and an azimuth quadrant and 'turquet' invented by him, at Meragha. He designed several instruments for Observatory such as Astrolabes, representations of constellation, epicycles, and shapes of spheres. Al-Tusi produced a very accurate table of planetary movements and a star catalogue, and he published it under the title 'Al-Zij-Ilkhani' which he dedicated to Halagu Khan. The book was the most popular book among astronomers until 15th century. Al-Tusi's memoir on astronomy 'Tadhkira fi Ilm al-Haya' includes his ingenious device for generating rectilinear motion along the diameter of the outer circle from two circular motions. Al-Tusi pioneered spherical trigonometry, which includes six fundamental formulas for the solution of spherical right-angled triangles. One of his most important mathematical contributions was the treatment of trigonometry as a new mathematical discipline. Al-Tusi's 'Akhlaq-i-Nasri' (Nasirean Ethics) was regarded as the most important on ethics and remained popular for centuries and 'Tajrid-al-'Aqaid' was an excellent work on Islamic scholastic philosophy. Al-Tusi being a prolific writer wrote in Arabic and Persian and his works were translated into Latin and other European languages in the Middle Ages. His book, 'Shaq al-Qatta' was translated into Latin entitled 'Figura Cata'. He translated Euclid into Arabic. Al-Tusi was born Abu Jafar Muhammad Ibn Muhammad Ibn al-Hasan Nasir al-Din al-Tusi at Tus, Khurasan (present Iran). He moved to Baghdad in 1274 and where he died.