The Hellenistic Ivan the Terrible (Lysimachus)
Lysimachus is often forgotten when it comes to the Diadochi, but he was actually one of the most important of Alexander’s successors—it’s just that his kingdom didn’t survive his death. He was charged with subduing Thrace, which took up most of his time. Eventually he would take the title of King of Thrace, following the other Diadochi.
His son, Agathocles, would emerge in the 290s as a formidable general and heir apparent, and according to our sources (Diodorus Siculus, Strabo, Plutarch) he and his father were close, and he was well liked in the Lysimachus-controlled provinces of Asia Minor. The sources differ on the cause of his execution but I lean towards the 70 year old Lysimachus falling into madness and the machinations of his wife, Agathocles’ step mother, who allegedly manufactured tales of Agathocles’ disloyalty, and plans to usurp his father. Other sources claim that the betrayal was genuine and imminent.
Lysimachus went through with it, regardless, putting his most capable son to death.
I think that the fact that Asia Minor immediately rose in revolt after Agathocles was executed points to the former theory, that Arsinoe was lying, trying to get her sons on the throne. Lysimachus was abandoned by many of his friends and generals after this hideous act.
Seleucus—both he and Lysimachus octogenarians by this point—took in Agathocles’ widow and used his death as a casus belli to invade Asia Minor. Lysimachus died in the battle that followed, and his short lived kingdom fell apart.