What is "onesicritus"

Onesicritus (; c. 360 BC – c. 290 BC), a Greek historical writer, who accompanied Alexander on his campaigns in Asia. He claimed to have been the commander of Alexander's fleet but was actually only a helmsman; Arrian and Nearchus often criticize him for this. When he returned home, he wrote a history of Alexander's campaigns. He is frequently cited by later authors, who also criticize him for his inaccuracies.