Euclid is the person credited with the invention of geometry. However the first uses of geometry are recorded to be over 5 thousand years old near the Indus Valley.
It is not known. Euclid's Elements is famous for setting out geometry in a systematic and axiomatic way, his book was by no means the first on geometry.
Because he was the first person to write a geometry book!
Erasthothenes
He was a geometrician and he was the first person to write a geometry book.
He is famous for his Elements, a presentation in thirteen books of the geometry and other mathematics known in his day.He also was the first person to study geometry.
Presumably at the birth of the Universe.
Pythagoras loved geometry.
He is the first person to set out geometry on a systematic basis starting from a small number of axioms. He was also responsible for developing the principles of geometric proof.
When the first person died.
Euclid
300bc