One of the greatest mathematicians of antiquity, Theodore was considered by his contemporaries as a geometrist of significant impact on mathematics. He was born in Cyrene of North Africa and was a contemporary of Hippocrates of Chios. Even though none of his works survive, it is known that Theodore was involved not just with geometry but also with irrational numbers.
Ancient writers account Theodore as a student of Protagoras and teacher of Plato in mathematics in Athens. It is postulated that when Plato went to Cyrene, he met Theodore, who taught him on irrational numbers. Most aspects of his life, including the exact date of birth and death, are unknown.
Credited by numerous ancient writers such as Xenophon, Jamblichus, Diogenes Laerius, Plato and Proclus as a master of his art, Theodore’s major contribution to mathematics was that he proved that the square roots of numbers 3,5,7,8,10… 17 are irrational numbers. How he was able to prove this is not known. It is hypothesized that he used geometry as a base for the proof. Furthermore, Theodore constructed the so-called Spiral of Theodorus, a spiral composed of right triangles placed edge to edge, which now bares his name.
As noted by Jamblichus, Theodore was a Pythagorean philosopher, initiated into the mysteries of Pythagoreanism. This comes to prove the high status he possessed at his time as a mathematician. In modern times, several mathematicians have successfully reproduced Theodore’s conclusions of the irrational numbers.
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