Gaius Julius Caesar Octavianus, formerly known simply as Gaius Octavian, is the son of Atia and adopted son and heir to Gaius Julius Caesar. He is based on real-life Augustus, an important politician of the Roman Republic and the first emperor of the Roman Empire.
Highly intelligent and well read, Octavian is a young man whose formidable strategic acuity distinguishes him from others, even among the upper classes of Rome. His astute understanding of those around makes him observant and lethally sharp in guessing the motives and intent of others. He is, however, cold and distant. He also displays a cynicism which is most likely a product of exposure to his amoral mother and the morally corrosive nature of Roman politics. He does however occasionally display his insecurities such as self-doubt in front of his sister (for whom he has sexual feelings) and Titus Pullo, to whom he admits his mediocre skills in physical combat, "I dare say I can kill a man, so long as he's not fighting back." He has already demonstrated this upon Pullo's rescue of him from being kidnapped by bandits hired by Pompey, when he beats to death an already heavily wounded bandit. His friendship with Pullo becomes a major plot point in the second season, with Octavian even entrusting to the soldier the assassination of the teenage Caesarion.
He is also well read in philosophy and is implied to be a monotheist and more specifically a deist (in contrast to his polytheistic society)--he does not believe in the Roman gods, but is open to the possibility of some kind of Prime Mover. He has political beliefs favoring rule by the people rather than the elite. Upon Lucius Vorenus asking why should the Republic be changed and the nobles out placed, Octavian counters by saying "Because the Roman people are suffering, because slaves have taken all the work, because nobles have taken all the land, and because the streets are filled with the homeless and the starving". Thus demonstrating a sense of compassion for the Roman people, but not so much for his own social class, the nobles.
In the second season, his opinions evolve; it becomes obvious that he intends to establish a tyranny, and he sincerely advocates a harsh stance on issues of moral degeneration amongst the Roman elite - particularly his own family, with whom he shares a tense and manipulative relationship, frequently using them for political gain. He also orders, along with Mark Antony, the assassination of nearly a thousand senators and rich citizens, including Cicero and the father of Jocasta, primarily to obtain their wealth and also to eliminate his opponents in the Senate. Atia herself personally admits privately that she is responsible for her son's cruelty, after years of manipulating Octavian he changed from a good and honest child. Despite this, he seems to be motivated by genuine benevolence for the Roman people and moral outrage at the corruption of Roman society.
He is shown to have sadistic sexual tendencies; he mentions this to his fiance Livia, rather ashamed, that when they are married he will sometimes beat her with his hands or a light whip, citing that it's not out of anger, but it gives him sexual pleasure. Luckily, not only does Livia tolerate his predilection, but also shares his pleasure in it; the two engage in erotic asphyxiation and particularly violent sex.
Born to one of the most powerful families in Rome, the Julii, Octavian is the only son and youngest child of Atia of the Julii. His father died when he was young and was subsequently brought up by his mother and his older sister, Octavia. At the beginning of the series Rome, Octavian is mere adolescent and his mother has him travel across a barren land with only a few slaves to take a white horse (brought to Rome by Timon), as a gift, to his great-uncle. However, along the way his slaves are killed and he is kidnapped by some Gaulish brigands. He is rescued by Titus Pullo and Lucius Vorenus and with them, they recover the golden eagle from Pompey's men and return it to Octavian's great-uncle, Julius Caesar. Caesar is extremely impressed with the young boy's strength, intelligence and common beliefs about the Plebeians.
Octavian returns to Rome, accompanied by Pullo and Vorenus under the command of Mark Antony, Atia's lover, and is taken home to his mother. He demonstrates a large understanding about the state of Rome and its politics. As the result of the rebellion, the Julii family and their allies prepare to commit suicide. Upon being asked who he would wish to kill him, Octavian states that, "I can take care of myself." Caesar returns to Rome and the Julii family are spared, leaving many of the other nobility to ask the protection from them. In the rebellion, Octavia's husband is killed, and although it would seem that Octavian suspects his mother is involved, he says nothing.
His mother is ambitious for Octavian's future, encouraging him to risk his life to impress his great-uncle, having him eat goat's testicles to make him more of a man, and enlisting Pullo as a tutor to help Octavian in his battle, as well as copulation skills. He is partly responsible for the deaths of Pompey's men and helping to murder Vorenus' brother-in-law, Evander Pulchio. Julius Caesar takes an interest in Octavian, giving him important political roles, including making him a pontiff despite his young age.
When Caesar's will is read shortly after his assassination it is revealed that he has adopted Octavian as his son and made him his heir. Octavian uses this to his full advantage and convinces Mark Antony to stay in Rome in order to stop Brutus and the other assassins from gaining power. However, after Brutus and the others flee Rome, Mark Antony refuses to transfer control of Caesar's money from Caesar's name to Octavian's. In retaliation against Antony and his mother, Octavian promises the plebeians the money that Caesar promised in the will. When Antony and Atia find out, he is attacked violently by Antony after Octavian insults his mother and refuses to apologize. Octavian is disgusted with his mother's choice of siding with Antony against him, and he runs away from home, taking all his belongings and a few soldiers. He travels south to Campania to stay with his friend Marcus Agrippa, who is well established there.
It is later mentioned that he and Agrippa have organized an army ten thousand strong that includes a large number of veterans. Cicero eventually sides with them against Antony, who is then declared a traitor. Very soon afterwards, Octavian is reunited with his friend Titus Pullo, who is amazed to see that the generals the Senate sent to led Octavian's soldiers have defeated Mark Antony. Pullo tells Octavian that Vorenus' children are alive and that he wanted to tell Vorenus, but he fought on Antony's side. Nonetheless, Octavian straight away insists that they find Vorenus, and gives him food, a horse and the seal of Caesar so that he might pass through the crowds. When Octavian returns to camp with Agrippa, they meet up with their friend Gaius Maecenas who informs them that the two generals who aided in defeating Antony have died and Octavian selfishly claims the victory is his. Although Octavian insists that the victory was not to spite Antony, it appears to be false and he intends to use his newfound power as influence in Rome, much to Cicero's fears.
The meeting between Octavian and Cicero is congenial, if not tense. Cicero adamantly refuses to give Octavian a triumph for his victory, claiming that Antony is still alive and thus a total victory was not achieved. However, at Octavian's insistence (along with some pressure from Agrippa), Cicero agrees to make Octavian consul provided that he listen to his advice. Octavian apparently agrees but then goes back on his promise when he declares Brutus and Cassius as enemies of the state (much to Cicero's chagrin). Due to the presence of armed soldiers in the Senate House, no one, not even Cicero, dares to oppose the measure and it is passed unanimously.
Octavian also continues to harbor a certain grudge against Atia for allowing Antony to beat him despite the pleas from Octavia to forgive their mother. Although Octavian is cold and stubborn, he seems to loosen up considerably when Atia personally asks for forgiveness. It remains to be seen whether Octavian truly forgives his mother. Eventually, Cicero brings forth a dilemma to Octavian. Brutus and Cassius have begun their march back to Rome with an alleged 20 legions (although Agrippa correctly guesses that this is an exaggeration) and will seek to remove Octavian. Octavian is initially quite distressed by the threat as he only has four legions but is quickly provided an answer by his mother. Going out to Cisalpine Gaul, Octavian (with some aid from Atia) creates an alliance with Antony in order to defeat Brutus and Cassius. While Antony proposes a direct attack, Octavian decides to first kill all supporters of Brutus before engaging in battle, Cicero being the most notable on his death list. Although the measure is greeted with shock by Lepidus, Antony enthusiastically adds the names of a couple of his own enemies onto the list and even Atia contributes. During the decisive Second Battle of Philippi, Octavian endures Antony's taunts with severe coldness and anxiously watches the battle while Antony impassively munches on a loaf of bread. When the battle reaches a critical turning point, Antony personally leads an attack while Octavian stays behind. Realizing that Antony would receive all the credit for a victory, Octavian sends Agrippa into battle as well. When the battle is finally over, Octavian notes with disgust that the smell of victory is nothing but "smoke, shit and rotting flesh".
In Death Mask, Atia suggests that the marriage between her and Mark Antony finally occur as a show of unity between Antony and Octavian. The men agree that such an arrangement is necessary as a marriage between their two houses would clearly make a strong political statement. However, to Atia's surprise it is her daughter Octavia who is betrothed to Antony. Understanding that Octavia's childbearing age makes her more suitable for the match, Atia goes along with the marriage — but is furious nonetheless. It was in this episode that Servilia of the Junii (mother to Brutus) cursed Atia prior to sacrificing her own life. Distraut from the recent news of Brutus' defeat at the second battle of Philippi, Servilia's curse pleaded to the gods for Atia to "taste nothing but ashes and iron" and for the remainder of her life to filled with "bitterness and despair".
Octavian's darker side emerges further in the episode A Necessary Fiction. He meets Livia, the young wife of Claudius Nero (and mother of his son, Tiberius), and decides that she will divorce her husband and marry him. He later confides in her that he may beat or lightly whip her during their marriage, but only because it brings him "sexual pleasure"; it is revealed in Deus Impeditio Esuritori Nullus that these sadomasochistic tendencies are mutual. When Maecenas reveals that Atia and Mark Antony have resumed their affair and that Octavia is involved with Agrippa, a furious Octavian invites them all to dinner. There he commands Antony to leave Rome indefinitely, or be publicly shamed with Octavia's adultery. He sends Atia and Octavia into seclusion (under armed guard) at Atia's villa, and solemnly forgives a shamed and remorseful Agrippa.
Antony begins his relationship with Cleopatra in Alexandria. Cleopatra urges Antony to declare war on Rome to combat Octavian's tyranny. Antony is hesitant, knowing that an attack on Rome would strip him of the people's devotion, the one thing that Octavian does not have. Instead Antony cuts off all grain shipments from Egypt to Rome. The plan works and greatly angers the starving Roman people who blame Octavian for the grain shortage. A desperate Octavian, facing riots and renewed civil war in Rome, responds by sending his sister Octavia and mother Atia to convince Antony to send grain. When Atia and Octavia arrive in Egypt Antony orders Lucius Vorenus to send them back Rome immediately. When both women strongly object Vorenus says that if they refuse to leave Egyptian soldiers will remove them by force. Antony begins to "go native" and embraces Egyptian culture.
With the assistance of Posca, he obtains Antony's will and orders it read aloud to the people of Rome, revealing that Antony had left control of the eastern provinces to his children with Cleopatra. The scandal is an appropriate casus belli, and after defeating Antony and Cleopatra at the Battle of Actium, he pursues them to Alexandria. There Antony descends into a drunken stupor and Octavian attempts to bargain with Cleopatra, hoping to display her as spoils of war at his triumph. He is foiled by their dual suicide; he sends Titus Pullo to assassinate Caesarion, but Pullo deceives him and saves the boy. The series ends with Octavian and his family attending his triumph, hailed as Caesar and savior of the Republic, at the dawn of the Empire.
- In Rome, Octavian becomes known as Gaius Octavian Caesar after Caesar's death. The real Octavian became known as Gaius Julius Caesar Octavianus (except by Cicero, who continued to address him as Octavian in order to amuse himself and dent Octavian's ego). He would go on to be known as Imperator Caesar Divi Filius Augustus, the first of the Roman Emperors.
- In Philippi Octavian does not object to Mark Antony's desire to proscribe and kill Cicero whereas historical sources indicate that Octavian only very reluctantly went along with Antony's wishes after two days of arguments and objections.
- In A Necessary Fiction, Octavian meets and plans to marry his first wife, Livia; historically, Octavian had already been married to and divorced Clodia Pulchra (daughter of Fulvia, wife of Mark Antony before Octavia) by this time. Furthermore, when Octavian met future wife Livia he was married to Scribonia, whom he divorced the same day she gave birth to his only child, Julia the Elder. Rome ignores these former relationships, but does acknowledge the existence of Livia's child, Tiberius Nero, by her first husband Tiberius Claudius Nero. Historically, Livia was pregnant with her second child Nero Claudius Drusus when she met Octavian, whom she married mere days after giving birth to her son.
- The personality of Octavian as presented in the show is different from that presented in the sources. Rome portrays Octavian as an emotionless and openly calculating member of the elite, while Suetonius presents him as more of a home-spun populist and a lover of other men's wives (including the wife of Maecenas, which led to their falling out). It is possible that both these portrayals are true to some extent, reflecting different facets of his persona. The eminent classicist Ronald Syme, whose work The Roman Revolution has been highly influential in the English-speaking world, famously called Octavian a 'chill terrorist'. But the position he put himself in, as Augustus, rebuilding Rome from deep division and near-catastrophe to peace and stability, necessitated the subtle and complex portrayal of a wide range of facets of personality, real and simulated. In the words of Julius Caesar's biographer, Christian Meier, Octavian "had to be an actor, and he knew this". Suetonius reports that on his deathbed, Augustus summoned his friends and asked them, "Did you like the performance?", referring to the play-acting and regal authority that he had put on as emperor. They assured him that they had and he replied, "Since I've played my part well, all clap your hands, and from the stage dismiss me with applause."
- Agrippa: We should have taken her [Cleopatra] there and then.
- Octavian: Why abduct her when she'll come on her own accord?
- Agrippa: And what if she follows Mark Antony instead, eh?
- Octavian: She betrayed Antony so that she might live, why would she lose heart now?
- Maecenas: You can have that effect on people.
- Octavian: I was all sweetness and light with her... charm itself.
- Maecenas: Yes, that is your most disheartening manner..