Hasan Ibn al-Haytham (Alhazen) was a scientist whose genius revolutionized our understanding of light and vision. In his 'Book of Optics,' he disproved the ancient Greek theory that the eye emits rays to see. Instead, he correctly argued that light reflects off objects and enters the eye. He was a pioneer of the scientific method, emphasizing experimental verification of theories. Al-Haytham experimented with the 'camera obscura,' explaining how light passing through a pinhole forms an inverted image. His work on lenses and mirrors laid the groundwork for the later invention of the telescope and microscope. He is often considered the world's first true scientist for his rigorous experimental approach.