Euclid is considered to be the father of geometry not because he was the first person who studied geometry. You could imagine the very first humans might have studied geometry. Many Greek mathematicians before Euclid did so many geometric things. But what made Euclid the father of geometry is really his writing of Euclid's Elements.
The pharaoh of Egypt, Ptolemy I, decided to learn geometry. He had a textbook, called "The Elements,” but he found this textbook difficult, so he asked the author of the book if there was an easier way to learn the subject. Euclid replied, "There is no royal road to geometry."
We don't know if Ptolemy ever succeeded in understanding Euclid's book, but we do know that for over 2000 years, people used "The Elements" to learn geometry. People often think "The Elements" was simply a geometry textbook. In fact, the book teaches much more. While its 13 chapters do teach plane and solid geometry, they also teach number theory and an old form of algebra. The Elements were arguably the most famous textbook of all time. In Elements, Euclid did a rigorous, thoughtful, logical march through geometry, number theory, and solid geometry.
Euclid took the mathematical knowledge of his age, organized it, and presented it in an orderly and logical way. He started with a set of axioms, and then used them to prove result after result. He was methodical. He was logical. He set a high bar for clear and structured thinking.
But who was this author, Euclid? What do we really know about the man who wrote the most successful textbook in history? Sadly, very little. We have no paintings or pictures of his face. We don't know when he was born or when he died. Yes, no one really knows what Euclid looked like.
We do know that Euclid was Greek, and that he worked in the great Library of Alexandria. Here he wrote and taught. Drawing shapes in the sand, he taught many to think logically, abstractly and geometrically.
That was around 300 BC. But Euclid's great book continued to be used for long after his death.
Euclid's Elements even helped a young Abraham Lincoln fine-tune his mind. Lincoln spoke of how it was Euclid who showed him what it truly meant to "demonstrate" - which was essential for his law studies.
Euclid influenced all kinds of great thinkers, not just mathematicians. And consider this - most of the books Euclid wrote were lost forever, when the Library of Alexandria tragically burned. We can only imagine what his legacy might have been if all his writings had survived the ages.