As military commander under King Philip II of Macedon, Attalus gained familial connection by marriage, becoming uncle to Eurydice (also called Cleopatra), one of Philip's wives. This marriage placed him within the Macedonian inner circle. At the wedding feast for Philip and Eurydice, Attalus declared the union would produce a "legitimate heir," directly challenging Alexander's status as Philip's recognized successor and implying Alexander's disqualification through his mother Olympias's Epirote/Molossian origins. Alexander reacted strongly to this perceived slight, publicly disowning Attalus as kin, triggering a confrontation with Philip that resulted in Alexander's temporary banishment. After Philip's assassination, Attalus commanded Macedonian forces battling Persian incursions on the edges of Persian territory during Alexander's early reign. However, his loyalty wavered amid the ensuing political instability; he began questioning his commitment to Macedonia and engaged in discussions with Persian representatives. This perceived shift toward Persia, combined with his prior hostility toward Alexander, culminated in his execution for treason. Macedonian loyalists ordered the execution after Alexander's ascension, serving as an early demonstration of the new king's resolve against internal threats. His death scene explicitly shows him being killed for conspiring with Persia against Macedonia.