Marcus Antonius (14 January 83 BC – 1 August 30 BC), commonly known in English as Mark Antony, was a Roman politician and general who played a critical role in the transformation of the Roman Republic from a constitutional republic into the autocratic Roman Empire.

Antony was a relative and supporter of Julius Caesar, and he served as one of his generals during the conquest of Gaul and Caesar's civil war. Antony was appointed administrator of Italy while Caesar eliminated political opponents in Greece, North Africa, and Spain. After Caesar's assassination in 44 BC, Antony joined forces with Lepidus, another of Caesar's generals, and Octavian, Caesar's great-nephew and adopted son, forming a three-man dictatorship known to historians as the Second Triumvirate. The Triumvirs defeated Caesar's killers, the Liberatores, at the Battle of Philippi in 42 BC, and divided the government of the Republic among themselves. Antony was assigned Rome's eastern provinces, including the client kingdom of Egypt, then ruled by Cleopatra VII, and was given the command in Rome's war against Parthia.

Relations among the triumvirs were strained as the various members sought greater political power. Civil war between Antony and Octavian was averted in 40 BC, when Antony married Octavian's sister, Octavia. Despite this marriage, Antony carried on a love affair with Cleopatra, who bore him three children, further straining Antony's relations with Octavian. Lepidus was expelled from the association in 36 BC, and in 33 BC, disagreements between Antony and Octavian caused a split between the remaining Triumvirs. Their ongoing hostility erupted into civil war in 31 BC when Octavian induced the republic to declare war on Cleopatra and proclaim Antony a traitor. Later that year, Antony was defeated by Octavian's forces at the Battle of Actium. Antony and Cleopatra fled to Egypt where, having again been defeated at the Battle of Alexandria, they died by suicide.

With Antony dead, Octavian became the undisputed master of the Roman world. In 27 BC, Octavian was granted the honorific title of Augustus, marking the final stage in the transformation of the Republic into a monarchy, with himself as the first Roman emperor.

A member of the plebeian gens Antonia, Antony was born in Rome on 14 January 83 BC. His father and namesake was Marcus Antonius Creticus, son of the noted orator Marcus Antonius who had been murdered during the purges of Gaius Marius in the winter of 87–86 BC. His mother was Julia, a third cousin of Julius Caesar. Antony was an infant at the time of Lucius Cornelius Sulla's march on Rome in 82 BC.

According to the Roman orator Marcus Tullius Cicero, Antony's father was incompetent and corrupt, and was only given power because he was incapable of using or abusing it effectively. In 74 BC he was given the military command to defeat the pirates of the Mediterranean, but he died in Crete in 71 BC without making any significant progress. The elder Antony's death left Antony and his brothers, Lucius and Gaius, in the care of their mother, Julia, who later married Publius Cornelius Lentulus Sura, an eminent member of the old patrician nobility. Lentulus, despite exploiting his political success for financial gain, was constantly in debt due to his extravagance. He was a major figure in the Catilinarian conspiracy and was summarily executed on the orders of the consul Cicero in 63 BC for his involvement.

According to the historian Plutarch, Antony spent his teenage years wandering through Rome with his brothers and friends gambling, drinking, and becoming involved in scandalous love affairs. Antony's contemporary and enemy, Cicero, charged that he had a homosexual relationship with Gaius Scribonius Curio. This form of slander was popular during this time in the Roman Republic to demean and discredit political opponents. There is little reliable information on his political activity as a young man, although it is known that he was an associate of Publius Clodius Pulcher and his street gang. He may also have been involved in the Lupercal cult as he was referred to as a priest of this order later in life. By age twenty, Antony had amassed an enormous debt. Hoping to escape his creditors, Antony fled to Greece in 58 BC, where he studied philosophy and rhetoric at Athens.^{[citation needed]}

In 57 BC, Antony joined the military staff of Aulus Gabinius, the Proconsul of Syria, as commander of the cavalry. This appointment marks the beginning of his military career. As consul the previous year, Gabinius had consented to the exile of Cicero by Antony's mentor, Publius Clodius Pulcher.