Theodorus of Samos (Greek: Θεόδωρος ο Σάμιος) was a 6th century BC ancient Greek sculptor and architect from the Greek island of Samos. Along with Rhoecus, he was often credited with the invention of ore smelting and, according to Pausanias, the craft of casting. He is also credited with inventing a water level, a carpenter's square, and, according to Pliny, a lock and key and the turning lathe. According to Vitruvius (vii, introduction), Theodorus is the architect of the Doric Order temple Heraion of Samos temple. In some texts he is described, above all, as a great artist and in some statues he is depicted as a great inventor.
Carl Sagan, in the episode "The Backbone of Night" from his series Cosmos, claims Theodorus invented the level, the ruler, the key, the square, the lathe, and bronze casting.
Of Samos, son of Rhoecus. In conjunction with his father, he erected the labyrinth of Lemnos (Pliny , Pliny H. N. xxxvi. 90), and advised the laying down of a layer of charcoal as part of the foundation of the Temple of Artemis at Ephesus (Diog. Laert. ii. 103). He is said to have lived for a long time in Egypt, where he and his brother Telecles learned the Egyptian canon of proportion for the human figure. He was considered by the Greeks as one of the inventors of the art of casting in bronze (Pausan. viii. 14, 8). He wrote a work on the Temple of Heré at Samos, which was begun by his father (Vitruv. vii. pref. 12).