[This book is about] the five so-called Platonic figures which, however, do not belong to Plato, three of the five being due to the Pythagoreans, namely the cube, the pyramid, and the dodecahedron, while the octahedron and the icosahedron are due to Theaetetus.You may know Theaetetus through Plato's dialog of the same name, where he's described as a mathematical genius. He's also mentioned in Plato's The Sophist. Theatetus seems to have worked on solid geometry between 380 and 370 BC, perhaps inspired by Plato's interest in the subject.
He died from battle wounds and dysentery in 369.