Ptolemy I Soter
According to the earliest source of information, the pseudepigraphic "Letter of Aristeas" composed between c180 and 145 BC, the library was initially organized by Demetrius of Phaleron, under the reign of Ptolemy I Soter (c.367 BC—c.283 BC). Other sources claim it was instead created under the reign of his son Ptolemy II (283–246 BC).