Sosthenes was a Macedon

Macedon

Macedonia or Macedon was an ancient kingdom, centered in the northeastern part of the Greek peninsula, bordered by Epirus to the west, Paeonia to the north, the region of Thrace to the east and Thessaly to the south....

ian and general and may have been a king of the Antipatrid dynasty

Antipatrid dynasty

The Antipatrid dynasty was a Macedonian dynasty founded by Cassander, the son of Antipater, who declared himself King of Macedon in 302 BC. This dynasty did not last long; in 294 BC it was overthrown by the Antigonid dynasty, whose members proved to be more effective rulers.Members of the...

. During the reign of Lysimachus

Lysimachus

Lysimachus was a Macedonian officer and diadochus of Alexander the Great, who became a basileus in 306 BC, ruling Thrace, Asia Minor and Macedon.-Early Life & Career:...

 he was his governor in Asia Minor

Asia Minor

Asia Minor is a geographical location at the westernmost protrusion of Asia, also called Anatolia, and corresponds to the western two thirds of the Asian part of Turkey...

. Sosthenes was elected King by the Macedonian army, but he may or not have reigned as king. Appointed as Strategos he may have declined the title of king as he had no royal connections. During his reign he faced invading Gauls, Antigonus Gonatas and other rivals. He defeated Bolgius, one of the earliest invading Gallic chiefs but was soon faced with the invasion of Brennus

Brennus (3rd century BC)

Brennus was one of the leaders of the army of Gallic invasion of the Balkans, defeated the assembled Greeks at Thermopylae, and is popularly reputed to have sacked and looted Delphi, although the ancient sources do not support this.In 280 BC a great army, comprising about 85,000 warriors, coming...

in the summer of 279 BC. Antigonus Gonatas tried to invade Macedonia from Asia in 278 but was beaten by Sosthenes.