Short answers, pulled from the story.
The Nerva-Antonine dynasty comprised seven Roman emperors: Nerva (96-98), Trajan (98-117), Hadrian (117-138), Antoninus Pius (138-161), Marcus Aurelius (161-180), Lucius Verus (161-169), and Commodus (177-192). The first five are popularly known as the Five Good Emperors.
The term derives from Niccolò Machiavelli's review of Roman emperors in Book 1, Chapter 10 of The Discourses on Livy. Machiavelli argued that emperors who succeeded by adoption were good, while those who inherited the throne by birth were generally bad.
Five of the six successions within the dynasty were accomplished through adoption rather than inheritance by birth, because the reigning emperor had no male heir. Under Roman law, adoption created a legal bond as strong as blood kinship, making the chosen successor a legitimate heir.
In The History of the Decline and Fall of the Roman Empire, Gibbon wrote that during their rule the Roman Empire was governed by "absolute power, under the guidance of wisdom and virtue." He saw their moderate policies as unusual compared to the more tyrannical and oppressive rulers who followed.
The dynasty ended with the murder of Commodus in 192 AD. His death triggered a period of turbulence known as the Year of the Five Emperors, which concluded with the establishment of the Severan dynasty.
Marcus Aurelius broke the dynasty's established pattern by naming his biological son Commodus as heir rather than adopting a chosen successor. This decision was considered an unfortunate choice and was seen as the beginning of the empire's decline.