Short answers, pulled from the story.
Antoninus Pius was Roman emperor from AD 138 to 161, the fourth of the Five Good Emperors from the Nerva-Antonine dynasty. Born Titus Aurelius Fulvus Boionius Antoninus on the 19th of September, 86, he was adopted by Emperor Hadrian on the 25th of February, 138, and reigned until his death on the 7th of March, 161.
The most likely reason is that Antoninus persuaded a reluctant Senate to grant divine honours to the deceased Emperor Hadrian, reflecting pietas or dutiful devotion. Two additional explanations circulated: that he physically supported his aging father-in-law at Senate meetings, and that he had convinced Hadrian to spare senators the ailing emperor had condemned to death.
The Antonine Wall was a Roman frontier barrier stretching 37 miles from the Firth of Forth to the Firth of Clyde in southern Scotland, shorter than Hadrian's Wall at 73 miles. It was constructed under governor Quintus Lollius Urbicus from 139 onward on orders from Antoninus Pius. The wall was gradually decommissioned in the mid-150s and abandoned in the early 160s; historians have speculated the campaign served partly to give Antoninus military prestige early in his reign.
Antoninus Pius left a public treasury of around 2.7 billion sesterces at his death in 161. The surplus was depleted almost immediately afterward due to the Antonine Plague, which soldiers brought back following a Parthian victory under Marcus Aurelius.
Antoninus Pius introduced the presumption of innocence into criminal proceedings, ruling that accused persons must not be treated as guilty before trial. He also established that trials and punishments must take place where the crime was committed, restricted the torture of slaves (prohibiting it for children under fourteen), and applied the principle of favor libertatis to favour freedom claims in uncertain cases of slavery.
The Hou Hanshu records that in 166 AD, a group arrived at the court of Emperor Huan of Han China claiming to be an embassy from 'Andun,' king of Daqin, a reference pointing to Antoninus. The text states it was the first direct contact between the two countries. Because Antoninus had died in 161, scholars debate whether the mission was sent by him or by his successor Marcus Aurelius, who also bore the name Antoninus; most evidence suggests the group were merchants rather than official ambassadors.