In Shakespeare's play, Portia's father is the famous Roman statesman Marcus Porcius Cato Uticensis, otherwise known as Cato the Younger. Cato was a notable rhetorician and a follower of Stoic philosophy, whose fame for integrity was widespread. Cato lamented the seeming decline in Roman values and other statesmen's willingness to compromise themselves for money or power. He frequently opposed Julius Caesar and the Triumvirate.

Plutarch tells a few stories of Cato as a child, all emphasizing his sense of rightness and his tenacity in doing what he deemed proper. He was unmoved by popular opinion and as an adult was admired in battle.

Cato died by suicide rather than accept what he believed was Caesar's tyranny. Plutarch describes an untidy attempt at the honorable style of Roman suicide by falling on one's swords, reporting that when others attempted to save Cato by administering care for his wound, he "plucked out his own bowels" and thus died.

Portia (or Porcia as her name is often spelled) was Cato's daughter by his first wife, Atilia. Shakespeare emphasizes her integrity and courage as the rightful inheritance of her father, who had a seemingly unswerving sense of what it meant to be a noble Roman.

Portia Catonis (70 BC-43 BC), usually known simply as Portia, was the second wife of Marcus Junius Brutus, the friend and assassin of Julius Caesar. Portia was the daughter of Marcus Porcius Cato Uticencis and his wife, Atilia. Portia's suicide is also well known, supposedly as a result of swallowing live, burning coals. Before her marriage to Brutus, she wed an ally of her father, Marcus Calpurnius Bibulus. They had a son, Lucius Calpurnius Bibulus, but there is some doubt that Portia actually gave birth to him, since she would have been between the ages of 11 and 17.