Cleomenes III () was King of Sparta in 235–222 BC. He succeeded to the Agiad throne of Sparta after his father, Leonidas II in 235 BC. From 229 BC to 222 BC, Cleomenes waged war against the Achaean League under Aratus of Sicyon. Domestically, he is known for his attempt to reform the Spartan state. After being defeated by the Acheans in the Battle of Sellasia in 222 BC, he fled to Ptolemaic Egypt. After a failed revolt in 219 BC, he committed suicide.