Ptolemy Keraunos (the Thunderbolt)

[Lysimachos]

Certainly one of the more unsavory characters of the Hellenistic period. However, I would note that the linked article has some inaccuracies. Notably, Agathocles was not the son of Arsinoe. He was the son of Lysimachus' first wife, Nicaea, while Arsinoe was his third wife. Agathocles and Arsinoe were, however, cousins both being grandchildren of Antipater. As too was Agathocles' wife, Lysandra, who was Arsinoe's sister. Confused yet?