Patroclus was a leading official, a fleet commander of the Ptolemaic navy  and admiral who served under Ptolemy II, best known for his activity during the Chremonidean War (267–261 BC). His early career is obscure, but it must have been distinguished enough for him to rise to the chief priesthood of Alexander and the Theoi Adelphoi in 271/270 BC. After the outbreak of the Chremonidean War, he led a diplomatic and military expedition to the Aegean Sea that expanded Ptolemaic control by establishing bases at Crete, Ceos, Thera, Attica and the Argolid. From these bases he tried, without much success, to aid the Athenians against Antigonus II Gonatas, King of Macedon. He may have been the defeated Ptolemaic commander at the Battle of Cos, which marked the end of Ptolemaic thalassocracy.