Ptolemy Keraunos (Ceraunus)(Πτολεμαίος Κεραυνός) (Keraunos: in Greek means "Thunder" or "Thunderbolt".)(? - 279 BC), King of Macedon from 281 BC to 279 BC.

He was the eldest son of Ptolemy I Soter (ruler of Egypt) and his third wife Eurydice (daughter of Antipater). His younger brother Ptolemy II. became heir apparent and, in 282 BC, the new pharaoh. Ptolemy Keraunos had left Egypt and arrived at the court of Lysimachus, the king of Thrace, Macedonia, and part of Asia Minor. His half-sister Arsinoe II of Egypt was wife of Lysimachus.

While staying in the court of Lysimachus, Keraunos sided with his sister in a court intrigue, and accompanied her to the court of Seleucus in the East to solicit his aid. Seeing an opportunity to intervene for his own gain in the politics of both Lysimachen Thrace and Ptolemiac Egypt, he prepared an expedition against Lysimachus shortly afterwards.

After Lysimachus' defeat and death in the battle of Corupedium in 281 BC, against Seleucus I Nicator, Ptolemy Keraunos murdered Seleucus I. In 281 BC he made an alliance with Pyrrhus of Epirus. Ptolemy asked his half-sister Arsinoe II, the widow of Lysimachus, to marry him. After the ceremony he killed Arsinoe's two younger sons and Arsinoe II herself fled to Egypt and married her own brother Ptolemy II.

Ptolemy Keraunos was killed in war against the Gauls of Brennus.

Death of Ptolemy Keraunos, 15th c. Medieval Manuscript France