World's Greatest Scientists

• Born: 780 AD, Khwarezm
• Died: 850 AD, Baghdad, Iraq
• Nationality: Iranian
• Books: The Compendious Book on Calculation by Completion and Balancing

Abū ʿAbdallāh Muḥammad ibn Mūsā al-Khwārizmī (Arabic: عَبْدَالله مُحَمَّد بِن مُوسَى اَلْخْوَارِزْمِي‎), earlier transliterated as Algoritmi or Algaurizin, (c. 780, Khwārizm – c. 850) was a Persian mathematician, astronomer and geographer during the Abbasid Empire, a scholar in the House of Wisdom in Baghdad.

In the twelfth century, Latin translations of his work on the Indian numerals introduced the decimal positional number system to the Western world. His Compendious Book on Calculation by Completion and Balancing presented the first systematic solution of linear and quadratic equations in Arabic. In Renaissance Europe, he was considered the original inventor of algebra, although it is now known that his work is based on older Indian or Greek sources. He revised Ptolemy's Geography and wrote on astronomy and astrology.

Some words reflect the importance of al-Khwarizmi's contributions to mathematics. "Algebra" is derived from al-jabr, one of the two operations he used to solve quadratic equations. Algorism and algorithm stem from Algoritmi, the Latin form of his name. His name is also the origin of (Spanish) guarismo and of (Portuguese) algarismo, both meaning digit.

• Born: July 1, 965 AD, Basra, Iraq
• Died: March 6, 1040, Cairo, Egypt
• Full name: Abu Ali al-Ḥasan ibn al-Ḥasan ibn al-Haytham
• Books: Book of Optics

Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham (Arabic: ابن الهيثم, Arabic: أبو علي، الحسن بن الحسن بن الهيثم‎, Latinized: Alhacen or (deprecated) Alhazen) (965 in Basra – c. 1040 in Cairo) was a Muslim scientist, polymath, mathematician, astronomer and philosopher, described in various sources as either an Arab or Persian. He made significant contributions to the principles of optics, as well as to astronomy, mathematics, visual perception, and to the scientific method. He also wrote insightful commentaries on works by Aristotle, Ptolemy, and the Greek mathematician Euclid.

He is frequently referred to as Ibn al-Haytham, and sometimes as al-Basri (Arabic: البصري), after his birthplace in the city of Basra. He was also nicknamed Ptolemaeus Secundus ("Ptolemy the Second") or simply "The Physicist" in medieval Europe.

Born circa 965, in Basra, present-day Iraq, he lived mainly in Cairo, Egypt, dying there at age 74. According to one version of his biography, overconfident about practical application of his mathematical knowledge, he assumed that he could regulate the floods of the Nile. After being ordered by Al-Hakim bi-Amr Allah, the sixth ruler of the Fatimid caliphate, to carry out this operation, he quickly perceived the impossibility of what he was attempting to do. Fearing for his life, he feigned madness and was placed under house arrest, during which he undertook scientific work. After the death of Al-Hakim he was able to prove that he was not mad, and for the rest of his life he made money copying texts while writing mathematical works and teaching. He is known as the "Father of Modern Optics, Experimental physics and Scientific methodology" and could be regarded as the first theoretical physicist.