**Official:**

Euclid. C. 300 B.C. Ancient Greek mathematician, author of the first surviving theoretical treatise on mathematics, “father of geometry.”

**Life and Work:**

1. Albert Einstein wrote about Euclid’s main work: “This admirable triumph of reasoning gave the human intellect the necessary confidence in itself for its subsequent achievements. If Euclid failed to kindle your youthful enthusiasm, then you were not born to be a scientific thinker.”

2. Little is known about the life of the author of the famous *The Elements*. Some historians of science compare Euclid with Nicolas Bourbaki or Kozma Prutkov. However, Euclid is not a collective pseudonym for a group of Alexandrian scientists. He was a mathematician who lived during the time of ruler of Egypt Ptolemy I Soter.

3. Little reliable information about Euclid’s life was drawn from ancient philosopher Proclus’ comments on the first book of The Elements. According to Proclus, Euclid was older than Archimedes, as Archimedes who was also a contemporary of Ptolemy I Soter used to mention Euclid. At the same time, Euclid was younger than Plato’s students and knew his philosophy well.

4. The Euclid name is translated from ancient Greek as “Good fame.” The scientist's fame is really good: he is considered the father of geometry. History has not known a textbook more successful: The Elements remained the main source of information on geometry from the time of its appearance and until the end of the 19^{th} century, and Euclid – an indisputable authority.

5. Many things collected in The Elements were the findings of Euclid's predecessors. One of the scientist’s most important achievements is that he tied ancient mathematicians’ works together and presented them logically and consistently.

6. The work considered to be the pinnacle of ancient mathematics consists of 13 books. They describe planimetry, stereometry, arithmetic, and the theory of numbers.

7. Each book of *The Elements* begins with definitions. In the first book, definitions are followed by common notions and postulates. Then it describes propositions divided into tasks to construct something and theorems to prove something. In total, 10 books of *The Elements* contain 130 definitions, five postulates, five common notions, 16 lemmas, and 465 theorems.

8. It is worth agreeing with Einstein: Euclid’s work is delightful. The beauty of the definitions at the beginning of the first book deserves admiration: “A point is that which has no part,” “A line is breadthless length,” “A straight line is a line which lies evenly with the points on itself.”

9. The story goes that Euclid used to end every mathematical reasoning with the Greek phrase “hoper edei deixai.” We know this phrase better as its Latin version “quod erat demonstrandum” or “which was to be proved” in Russian.

10. The great antique scientist’s other surviving works are Data, On Division of Figures, Phaenomena, Optics and several other works the authorship of which is disputed.

11. In addition to mathematical works, historical anecdotes related to Euclid are survived. The story about the conversation between the ancient Greek mathematician with Egyptian king Ptolemy I became widely known. The august person wondered whether it was possible to master geometry without exhausting studies. “There is no royal road to geometry!” Euclid answered bitingly.

12. Euclid is mentioned by mathematician and engineer of the 3^{rd}-4^{th} century Pappus of Alexandria and Byzantine writer of the 5^{th} century Joannes Stobaeus. Pappus claimed that Euclid was kind to anyone who could contribute to the development of mathematical sciences even in the slightest degree. In his turn, Stobaeus described another anecdote about Euclid. A young man who started studying geometry and analyzed his first theorem asked Euclid: “But what shall I get by learning these things?” Euclid called a slave and said: “Give him three obols, since he must make gain out of what he learns.”