**Euclid of Alexandria** (Ancient Greek: Εὐκλείδης – *Eukleídēs*, lived c. 300 BCE, Alexandria, Egypt) systematized ancient Greek and Near Eastern mathematics and geometry. He wrote *The Elements*, the most widely used mathematics and geometry textbook in history. Older books sometimes confuse him with Euclid of Megara.

Modern economics has been called “a series of footnotes to Adam Smith,” who was the author of *The Wealth of Nations* (1776 CE). Likewise, much of Western mathematics has been a series of footnotes to Euclid, either developing his ideas or challenging them.