What theories did Euclid make?

Euclid, often referred to as the "Father of Geometry," is best known for his work "Elements," which systematically presented the principles of geometry. In this comprehensive compilation, he introduced foundational concepts such as points, lines, and planes, and established the axiomatic approach to geometry, where propositions are derived from a small set of axioms. Euclid also explored theories related to number theory, including the properties of prime numbers and the Euclidean algorithm for finding the greatest common divisor. His influence extends beyond mathematics, shaping logical reasoning and deductive structure in various fields.