This statement (taken probably from Geminus) may perhaps rest on the fact that Theaetetus was the first to write at any length about the two last-mentioned solids. We are told indeed by Suidas that Theaetetus "first wrote on the 'five solids'" as they are called.Geminus of Rhodes was a Greek astronomer and mathematician who worked during the 1st century BC. It is believed that one lineage of copies of the Elements contains his marginal notes.
Suidas was a Greek lexicographer who lived about 970 AD. Jowett — famous classicist and translator of Plato — writes:
There is no reason to doubt that Theaetetus was a real person.... But neither can any importance be attached to the notices of him in Suidas and Proclus, which are probably based on on the mention of him in Plato. According to a confused statement in Suidas, who mentions him twice over, first, as a pupil of Socrates, and then of Plato, he is said to have written the first work on the Five Solids. But no early authority cites the work...