Abu ?Ali al-?asan ibn al-?asan ibn al-Haytham (Arabic: ??? ???? ????? ?? ????? ?? ??????; Persian: ??? ????; Latinized: Alhacen or Alhazen; 965 in Basra - c. 1040 in Cairo) was a Muslim; Persian or Arab scientist and polymath. He is frequently referred to as Ibn al-Haytham; and sometimes as al-Basri (Arabic: ??????); after his birthplace in the city of Basra.

Alhazen made significant contributions to the principles of optics; as well as to physics; astronomy; mathematics; ophthalmology; philosophy; visual perception; and to the scientific method. He was also nicknamed Ptolemaeus Secundus ('Ptolemy the Second') or simply 'The Physicist' in medieval Europe. Alhazen wrote insightful commentaries on works by Aristotle; Ptolemy; and the Greek mathematician Euclid.

Born circa 965; in Basra; Iraq; he lived mainly in Cairo; Egypt; dying there at age 76. Over-confident 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; and retired from engineering.

Fearing for his life; he feigned madness and was placed under house arrest; during and after which he devoted himself to his scientific work until his death.