Theodorus of Cyrene

Theodorus of Cyrene was an ancient Greek mathematician who was active around 450 BC. Almost everything known about him comes from Plato, whose dialogues the Theaetetus, the Sophist and the Statesman are the only first-hand accounts that survive. He was born in the colony of Cyrene on the northern coast of Africa and apparently taught both there and in Athens. A weak tradition repeated by ancient biographers such as Diogenes Laertius says Plato later studied with him in Cyrene. In the Theaetetus he is said to have proved that the square roots of the integers from 3 up to 17 are irrational, which is often thought to be the construction now called the Spiral of Theodorus. The same dialogue suggests that his pupil Theaetetus then built a more general theory of irrational square roots. Little more can be said of his life with confidence.