Various tests are applied to Claudius Ptolemy's long-suspect claim that he himself observed the more than 1000 objects in the Ancient Star Catalog. An obvious consequence of observing under the influence of Ptolemy's large equinox-position error is found not to exist in the Catalog. The true observer's latitude, rough epoch, and probable identity are discovered. Hitherto-lost details of his fundamental work are reconstructed, including the earliest known accurate observation of the obliquity (135 B.C.).