The Pythagorean Theorem is named after the ancient Greek mathematician Pythagoras, who is credited with discovering and proving the relationship between the sides of a right-angled triangle. This theorem states that in a right triangle, the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the lengths of the other two sides. The name "Pythagorean Theorem" is a testament to Pythagoras's significant contribution to the field of geometry.

The naming of the theorem after Pythagoras is not solely due to his discovery; it also reflects the historical context of mathematical knowledge. During the time of Pythagoras, the theorem was already known and used by the Babylonians and the Egyptians. However, it was Pythagoras who provided the first recorded proof of the theorem, which is why his name is associated with it. The theorem's significance was further solidified by Pythagoras's involvement in the development of Pythagoreanism, a philosophical and religious movement that emphasized the importance of mathematics in understanding the universe.

Historical evidence suggests that the theorem was known to the Babylonians as early as 1800 BCE, and the Egyptians had a similar understanding of the relationship between the sides of a right triangle. Despite this, it was Pythagoras who is credited with the first known proof of the theorem, which he presented in his treatise "On the Right-Angled Triangle." This proof, known as the Pythagorean proof, is a cornerstone of Euclidean geometry and has been used for centuries to solve various mathematical problems.

The naming of the theorem after Pythagoras also highlights the importance of individual contributions in the development of mathematical knowledge. In the ancient world, mathematics was often associated with the gods, and the discovery of the Pythagorean Theorem was seen as a divine revelation. By naming the theorem after Pythagoras, the ancient Greeks were acknowledging his role in uncovering this profound mathematical truth.

In conclusion, the Pythagorean Theorem is named after Pythagoras due to his discovery and proof of the relationship between the sides of a right-angled triangle. The naming reflects the historical context of mathematical knowledge and the importance of individual contributions in the field. The theorem's significance is further underscored by its use in Euclidean geometry and its enduring relevance in various mathematical applications.