It was firmly believed in India that he who owned Koh-i-Noor would rule the world. When the Persian, Nadir Shah, sacked Delhi in 1739 this diamond became one of his objectives. The tale is told that the defeated Mogul hid the diamond in his turban. Nadir, learning of this, invited the conquered Mogul to a feast and then forced him to exchange turbans. The moment the Moguls turban was in his hand, Nadir unwound it and the diamond fell out. At which moment Nadir is said to have cried out, Mountain of Light! and this is the legend of how the diamond acquired its name.

—S. Tolansky, from The History and Use of Diamond, 1962.