Theodorus of Cyrene (‹See Tfd›Greek: Θεόδωρος ὁ Κυρηναῖος, translit. Theódōros ho Kyrēnaîos; fl. c. 450 BC) was an ancient Greek mathematician. The only first-hand accounts of him that survive are in three of Plato's dialogues: the Theaetetus, the Sophist, and the Statesman. In the former dialogue, he posits a mathematical construction now known as the Spiral of Theodorus.