Hephaestion was a Macedonian nobleman and a distinguished general in Alexander the Great's army, born around 356 BC. He shared his upbringing with Alexander and was considered his dearest friend, with their bond often compared to that of Achilles and Patroclus. His military career was extensive, involving him in diplomatic missions, river crossings, sieges, and the establishment of new settlements throughout Alexander's campaigns. He also engaged with philosophers like Aristotle and supported Alexander's efforts to merge Greek and Persian cultures. Alexander appointed him second-in-command and arranged his marriage to Drypetis, sister of Alexander's second wife, thus making him part of the royal family. His sudden death in 324 BC at approximately 32 years of age deeply affected Alexander, who sought divine honors for him and planned lasting memorials.

Born around 356 BC, Hephaestion's exact age is unknown, but he is presumed to be a contemporary of Alexander the Great. He likely entered court as a page, a common role for aristocratic Macedonian boys. His close friendship with Alexander suggests he may have studied under Aristotle at Mieza, a period when Alexander was around fifteen. Evidence for this includes his name appearing in Aristotle's correspondence catalog, indicating a significant level of education and intellectual engagement. Unlike some of Alexander's older companions, Hephaestion was not exiled during the Pixodarus affair, possibly due to his age and perceived lesser threat to Philip II's authority. This suggests he maintained his position within Alexander's inner circle from a young age.

Hephaestion's military training began early, likely learning to fight and ride from childhood. His early campaigns may have included conflicts in Thrace and against Philip II. His career gained prominence during Alexander's invasion of Persia. He undertook important diplomatic missions, such as appointing a new ruler for Sidon after the Battle of Issus. He also commanded Alexander's fleet along the Phoenician coast and was tasked with logistical challenges, including the transport and reassembly of siege engines. His correspondence with Alexander, even when separated on missions, highlights their close relationship and Alexander's trust in his judgment. Hephaestion's involvement in potential reconciliation efforts between Alexander and figures like Demosthenes, as well as his role in securing the Euphrates crossing, underscore his multifaceted responsibilities.

Hephaestion played a significant role in Alexander's efforts to integrate Persian and Greek populations. Following the Battle of Gaugamela, where he was noted as commander of the bodyguards and was wounded, he assisted Alexander in verifying the lineage of Persian prisoners, demonstrating tact and sympathy towards noble families. He was also instrumental in enforcing Alexander's policies, even in matters of punishment, such as participating in the torture and execution of Philotas. After Philotas's downfall, Hephaestion was appointed joint commander of the Companion cavalry, a position that reflected a balance between factions within the army: those, like Hephaestion, who supported integration, and older veterans who harbored resentment towards Persian customs. This dual command structure aimed to manage these differing perspectives within Alexander's forces.

Hephaestion died suddenly in Ecbatana around the age of thirty-two. His death caused Alexander profound grief, leading him to petition the oracle at Siwa for Hephaestion to be granted divine status, resulting in his veneration as a Divine Hero. Hephaestion was cremated, and his ashes were transported to Babylon. At the time of Alexander's own death just eight months later, he was still actively planning extensive monuments to commemorate Hephaestion's memory. This indicates the deep and lasting impact Hephaestion had on Alexander, both personally and as a key figure in his empire.