Demetrius I was a king of the ancient Greek kingdom of Macedonia, ruling from 239 to 229 BCE. He was a member of the Antigonid dynasty and is known for his efforts to strengthen his kingdom during a time of political instability. His reign was marked by military campaigns and attempts to consolidate power in the region. Demetrius I faced challenges from rival factions and external threats, including the Aetolian League and Epirus. Despite his efforts, his reign ended in turmoil, leading to his eventual downfall. His legacy is often overshadowed by the subsequent rulers of Macedonia and the changing political landscape of the Hellenistic world.