Cleomenes II

Cleomenes II (in Greek: Κλεομένης ) was the king of Sparta (current-day Southern Greece) possibly from around 370 to around 309 BC. Almost nothing is known about his reign, or activities in general. Since many other high-ranking people from the same area and time-period have been extensively documented, some historians have labelled him a 'prodigious non-entity'.

Various theories have been suggested to explain his very noticable lack of documentation, but none has been generally accepted.

There is also confusion regarding how long he reigned :

Diodorus 15.60.5, under the year 370 BC, informs us that the Agiad Kleomenes II became king of Sparta at that date and reigned for 34 years (i.e. to 336/5). At 20.29.1, under the year 309, he records his death and tells us that he reigned for 60 years and ten months. To die once may be counted a misfortune; to die twice looks very much like carelessness on the part of Diodorus."

Source : The Length of the Reigns of Kleomenes ^{[ paywalled ]} David Harvey, Historia: Zeitschrift für Alte Geschichte Bd. 58, H. 3 (2009), pp. 356-357