Agathocles (Greek: Ἀγαθοκλῆς, flourished 3rd century BC, died 203/202 BC) was a Ptolemaic minister and together with his sister Agathoclea were very close to Egyptian Greek King Ptolemy IV Philopator who reigned 221 BC–205 BC.
Agathocles through his father was a distant relation of the Ptolemaic dynasty. Agathocles was the son born to Oenanthe of Egypt from her first husband Agathocles and also had two unnamed sisters. His paternal grandmother Theoxena of Egypt, was a Syracusan princess and Theoxena’s mother, also named Theoxena was a Macedonian noblewoman, who was the second older maternal half-sister of Ptolemy II Philadelphus, who reigned 283 BC-246 BC. Polybius states he had other relations who served the Ptolemaic dynasty: Nico or Nicon, a nauarch under Ptolemy IV; Philo and Philammon, appointed Libyarch of Cyrene by himself.
Agathocles and his sister were introduced to Ptolemy IV by their ambitious mother. Despite Ptolemy IV marrying his sister Arsinoe III in 220 BC, Agathoclea continued to be his favourite. According to surviving inscriptions in 216/215 BC, Agathocles served as eponymous priest of the Ptolemaic cult of Alexander the Great. On the death of Ptolemy IV in 205 BC, Agathocles and his allies kept the event secret, that they might have an opportunity to plunder the royal treasury. They also formed a conspiracy with Sosibius aimed at placing Agathocles on the throne or at least making him regent for the new boy king, Ptolemy V Epiphanes. With the support of Sosibius, they murdered Arsinoe III. Agathocles then acted as guardian to the young king Ptolemy V Epiphanes.