Pappus of Alexandria was a Greek mathematician who lived and worked in the 4th century CE. He was active in Alexandria, Egypt, which remained a major center for scientific study during the late Roman Empire. The date of his activity is established from his own writings, where he records observing a solar eclipse in Alexandria in 320 CE. Very few other biographical details about his life are known.

His most important surviving work is the Collection (in Greek, Synagōgē), a large compendium of Greek geometry. While parts are lost, the existing text is not just a simple compilation. According to modern scholars, Pappus added original explanations, extensions of theorems, and alternative proofs. This work preserves many mathematical ideas and methods from earlier giants like Euclid, Archimedes, and Apollonius, whose own works are now partially lost. The Collection addresses famous problems, such as doubling the cube, and contains an early version of what is now called Pappus's centroid theorem. He also wrote a commentary on Ptolemy's Almagest, but it survives only in fragments.

Pappus's historical importance is as a preserver and systematizer of classical Greek mathematics. His Collection is a crucial source for understanding the scope and techniques of ancient geometry. It served as a key link in transmitting this knowledge, influencing later Byzantine scholars and, after being translated into Latin in the 1500s, early modern European mathematicians like Johannes Kepler.