Titus Aurelius Fulvus Boionius Arrius Antoninus, generally known as Antoninus Pius, reigned from 138 to 161. He was the fourth of the Five Good Emperors and a member of the Aurelii gens. He was not called "Pius" until after his accession to the throne. Almost certainly, he earned the name "Pius" because he compelled the Senate to deify the late emperor Hadrian.

He was the son and only child of Titus Aurelius Fulvus, consul in 89 whose family came from Nemausus (modern Nîmes) and was born near Lanuvium and his mother was Arria Fadilla. Antoninus' father and paternal grandfather died when he was young and he was raised by Titus Arrius Antoninus, his maternal grandfather.

As a private citizen between 110 and115, he married Annia Galeria Faustina the Elder. She spent her whole life caring for the poor and assisting the most disadvantaged Romans. Faustina bore Antoninus four children, two sons and two daughters.

Having filled with more than usual success the offices of quaestor and praetor, he obtained the consulship in 120; he was next appointed by the Emperor Hadrian as one of the four proconsuls to administer Italia, then greatly increased his reputation by his conduct as proconsul of Asia. He acquired much favor with the Emperor Hadrian, who adopted him as his son and successor on February 25, 138.

On his accession, Antoninus' name became "Imperator Caesar Titus Aelius Hadrianus Antoninus Augustus Pontifex Maximus". One of his first acts as Emperor was to persuade the Senate to grant divine honours to Hadrian, which they had at first refused; his efforts to persuade the Senate to grant these honours is the most likely reason given for his title of Pius (dutiful in affection; compare pietas).

He built temples, theaters, and mausoleums, promoted the arts and sciences, and bestowed honours and financial rewards upon the teachers of rhetoric and philosophy.

In marked contrast to his predecessors Trajan and Hadrian, Antoninus was not a military man. His reign was the most peaceful in the entire history of the Principate. The unrest in Britannia is believed to have led to the construction of the Antonine Wall from the Firth of Forth to the Firth of Clyde, although it was soon abandoned.

After the longest reign since Augustus, Antoninus died of fever at Lorium in Etruria, about twelve miles (19 km) from Rome, giving the keynote to his life in the last word that he uttered when the tribune of the night-watch came to ask the password - "aequanimitas" (equanimity). His body was placed in Hadrian's mausoleum, a column was dedicated to him on the Campus Martius, and the temple he had built in the Forum in 141 to his deified wife Faustina was rededicated to the deified Faustina and the deified Antoninus.

His successor Marcus Aurelius in his "The Meditations" Book One paragraph 16, writes about his step-father:

"And I observed that he had overcome all passion for boys".