Euclid of Alexandria is one of the most important and influential mathematicians in history. Living in ancient Alexandria, he wrote The Elements, a geometry textbook used in some places until the twentieth century. His work in geometry provided the foundation on which all future mathematicians were educated.
For a man of such great significance to the world of mathematics, little is known about his actual life. Euclid is thought to have lived from 325-265 BC, mostly in Alexandria. He was taught at The Academy in Athens, founded by Plato, and probably tutored another great mathematician, Archimedes. Euclid also founded a great mathematics school in Alexandria. Little was ever written about Euclid, and the available information is scarce and of questionable accuracy. Much of the information we do have is from authors like Proclus who lived centuries later, writing about his books, not his life.
If little has ever been made of Euclid's life, then the opposite is true of his book. The Elements was used as the primary geometry resource for over 2000 years, and his lessons could still be used today. Although it contains 13 volumes, much of the work may not be Euclid's. Some of the chapters seem to be written with different styles, and others are geared for different ages, leading one to believe that he inserted other mathematicians' work into his own.
Each volume begins with pages of definitions and postulates, followed by his theorems. Euclid then proves each one of his theorems using the definitions and postulates, mathematically proving even the most obvious. His work was translated into Latin and Arabic, and was first printed in mass quantity in 1482, ten years before Columbus, but 1800 years AFTER it was written! From that point until the early 1900's, The Elements was considered by far the best geometry textbook in the world.
Although he may not have written The Elements entirely on his own, his other works are certainly his alone. Those include Data, Optics, Phaenomena, and On Division of Figures. His work in Data is probably the most famous of his smaller works, and focuses on finding certain measurements and quantities when others are given. Phaenomena is about planetary motions and Optics about perspectives. In Optics, Euclid attempts to prove the common belief of the time that sight was created by rays coming from the eye, rather than light entering the eye.
Euclid was apparently a kind, patient man, and did possess a sarcastic sense of humor. In fact, King Ptolemy once asked Euclid if there was an easier way to study math than learning all the theorems. Euclid then replied, "There is no royal road to geometry," and sent one of the most powerful kings of his time off to study. On another occasion, a student of his questioned the value of learning geometry, much like students today. Euclid responded by giving the small child a coin, saying that "he must make gain out of what he learns."
There are many other works of Euclid which appear to be lost to time, but his primary work in The Elements is what made him famous. His work in geometry led to discovery after discovery in history, and provided the basis for mathematical education for 2000 years. While students no longer read directly from his writing, the textbooks of today are still based on Euclidean proofs and theorems. Perhaps it is fitting, then, that Euclid is called "The Father of Geometry."
Sources: 1. Euclid, http://www.crystalinks.com/euclid.html. 26 Jan 2003.
2. Euclid of Alexandria. School of Mathematics and Statistics, University of St Andrews, Scotland. http://www-groups.dcs.st-and.ac.uk/history/Mathematicians/Euclid.html. 24 Jan 2003.
3. Euclid, Greek Mathematician. The Columbia Encyclopedia, 2001. http://www.bartleby.com/65/eu/Euclid.html.