Alcibiades was an Athenian-born man, student and rumored lover of Socrates, who graduated from normal hoplite to cavalry to supreme commander of Athen's military forces.
Alcibiades was just 17 when the Peloponnesian War broke out between the Delian League, led by Athens, and the Peloponnesian League, led by Sparta. Alcibiades was charismatic, but also rowdy and self-aggrandizing. He found his way into power and supported an aggressive stance against their enemy, Sparta.
However, his main political rival, Nicias, formed a peace with Sparta in the middle of the war. It was meant to last 50 years, but hardly lasted 5. Many of Sparta's allies, such as Corinth and Megara, refused to sign the peace. Additionally, Alcibiades and other democrats in Athens sought to cripple Sparta. Using his position of power, Alcibiades made many aggressive moves that led to the resurgence of the war.
The real event that kickstarted the war once more was the Sicilian Expedition, in which Athens sent troops to fight against a Spartan ally in Syracuse. Alcibiades, Nicias, and another general named Lachamus were all sent to oversee the expedition. However, the defacing of several religious statues, seen as treason by the Athenians, was blamed on the rowdy Alcibiades and his friends. After the expedition set sail, Alcibiades was sent back to stand trial. Instead of following obediently back to Athens in a ship, he escaped to Sparta. He offered his sword and told Sparta the Athenian plan in exchange for security. Alcibiades' trial was held in his absence, where he was pronounced guilty of treason and sentenced to death.
Alcibiades stayed in Sparta and offered their military advice for quite some time; however, his reception there grew more hostile. He was suspected of fathering a child with the wife of one of the kings, and therefore fled Sparta to escape a possible assasination attempt.
From there, Alcibiades sought to endear himself to the Persians. The Persians, who had fought and lost to the Greek city-states earlier in the Greco-Persian Wars, were content to watch the battle play out and see the city-states weaken each other. They eventually began selling troops and supplies to Sparta, since Athens had claimed parts of formerly Persian territory in Asia Minor. However, Alcibiades plotted to return to Athens even as he helped the Persians.
Alcibiades figured he would find more support amongst the Athenian oligarchs, the opposing faction to the democrats. He promised Persian support should he be recalled into Athens. However, Persia offered no such assistance, as Alcibiades had presumably suspected would happen. Despite his failure to deliver and the eventual return of the democratic faction to power, Alcibiades was reinstated and remained an Athenian general. Alcibiades, though he claimed time and again his friendliness with the Persians, was imprisoned in Persia once he sailed out to meet the Persian troops with gifts. He escaped and fled back to Athens, his claim of an alliance with Persia no longer holding any water.
He oversaw more military victories over Sparta, but was brought down by a significant defeat, in which he left his main troops in someone else's hands. When Athens lost the fight by a large margin, Alcibiades' opponents removed him from power and Alcibiades went into self-imposed exile. Thereafter, Alcibiades tried to advise Athens once more, but was ignored. By ignoring his advice, however, Athens lost a major battle and much morale. Athens would lose the war within 2 years.
Alcibiades sought refuge in Persia once more, and while accounts of his death differ, some suggest a Spartan general tracked him down and set fire to his house.