Praetorian Guard in the context of "Galba"

Trajan (/ˈtreɪdʒən/ TRAY-jən; born Marcus Ulpius Traianus, 18 September 53 – c. 9 August 117) was a Roman emperor from AD 98 to 117, remembered as the second of the Five Good Emperors of the Nerva–Antonine dynasty. He was a philanthropic ruler and a successful soldier-emperor who presided over one of the greatest military expansions in Roman history, during which, by the time of his death, the Roman Empire reached its maximum territorial extent. He was given the title of Optimus ('the best') by the Roman Senate.

Trajan was born in the municipium of Italica in the present-day Andalusian province of Seville in southern Spain, an Italic settlement in Hispania Baetica; his gens Ulpia came from the town of Tuder in the Umbria region of central Italy. His namesake father, Marcus Ulpius Traianus, was a general and distinguished senator. Trajan rose to prominence during the reign of Domitian; in AD 89, serving as a legatus legionis in Hispania Tarraconensis, he supported the emperor against a revolt on the Rhine led by Antonius Saturninus. He then served as governor of Germania and Pannonia. In September 96, Domitian was succeeded by the elderly and childless Nerva, who proved to be unpopular with the army. After a revolt by members of the Praetorian Guard, Nerva decided to adopt as his heir and successor the more popular Trajan, who had distinguished himself in military campaigns against Germanic tribes.

Marcus Aurelius Antoninus (born Lucius Septimius Bassianus, 4 April 188 – 8 April 217), better known by his nickname Caracalla (/ˌkærəˈkælə/; Latin: [karaˈkalːa]), was Roman emperor from 198 to 217 AD, first serving as nominal co-emperor under his father and then ruling alone after 211 AD. He was a member of the Severan dynasty, the elder son of Emperor Septimius Severus and Empress Julia Domna. Severus proclaimed Caracalla co-ruler in 198, doing the same with his other son Geta in 209. The two brothers briefly shared power after their father's death in 211, but Caracalla soon had Geta murdered by the Praetorian Guard and became sole ruler of the Roman Empire. Julia Domna had a significant share in governance, since Caracalla found administration to be mundane. His reign featured domestic instability and external invasions by the Germanic peoples.

Caracalla issued the Antonine Constitution (Latin: Constitutio Antoniniana), also known as the Edict of Caracalla, which granted Roman citizenship to all free men throughout the Roman Empire. The edict gave all the enfranchised men Caracalla's adopted praenomen and nomen: "Marcus Aurelius". Other landmarks of his reign were the construction of the Baths of Caracalla, the second-largest bathing complex in the history of Rome, the introduction of a new Roman currency named the antoninianus, a sort of double denarius, and the massacres he ordered, both in Rome and elsewhere in the empire. In 216, Caracalla began a campaign against the Parthian Empire. He did not see this campaign through to completion due to his assassination by a disaffected soldier in 217. Macrinus succeeded him as emperor three days later.

Tiberius Claudius Caesar Augustus Germanicus (/ˈklɔːdiəs/ KLAW-dee-əs; Classical Latin: [tɪˈbɛri.ʊs ˈkɫau̯di.ʊs ˈkae̯sar au̯ˈɡʊstʊs ɡɛrˈmaːnɪkʊs]; 1 August 10 BC – 13 October AD 54), or Claudius, was a Roman emperor, ruling from AD 41 to 54. A member of the Julio-Claudian dynasty, Claudius was born to Drusus and Antonia Minor at Lugdunum in Roman Gaul, where his father was stationed as a military legate. He was the first Roman emperor to be born outside Italy.

As he had a limp, a stammer, and a tremor due to an illness he suffered when young, he was ostracized by his family and was excluded from public office until his consulship (which was shared with his nephew, Caligula, in 37). Claudius's infirmity probably saved him from the fate of many other nobles during the purges throughout the reigns of Tiberius and Caligula, as potential enemies did not see him as a serious threat. His survival led to him being declared emperor by the Praetorian Guard after Caligula's assassination, at which point he was the last adult male of his family.

Marcus Aurelius Antoninus (born Sextus Varius Avitus Bassianus, c. 204 – 13 March 222), better known by his posthumous nicknames Elagabalus (/ˌɛləˈɡæbələs/ EL-ə-GAB-ə-ləs) and Heliogabalus (/ˌhiːliə-, -lioʊ-/ HEE-lee-ə-, -⁠lee-oh-), was Roman emperor from 218 to 222, while he was still a teenager. His short reign was notorious for religious controversy and alleged sexual debauchery. A close relative to the Severan dynasty, he came from a prominent Syrian Arab family in Emesa (Homs), Syria, where he served as the head priest of the sun god Elagabal from a young age. After the death of his cousin, the emperor Caracalla, Elagabalus was raised to the Principate at 14 years of age in an army revolt instigated by his grandmother Julia Maesa against Caracalla's short-lived successor, Macrinus. He only posthumously became known by the Latinised name of his god.

Elagabalus is largely known from accounts by the contemporary senator Cassius Dio who was hostile to him, Herodian, who likely relied extensively on Dio, and the much later Historia Augusta. The reliability of the accounts of Cassius Dio and the Historia Augusta, particularly their most salacious elements, has been questioned. Elagabalus showed a disregard for Roman religious traditions. He brought the cult of Elagabal (including the large baetyl stone that represented the god) to Rome, making it a prominent part of religious life in the city. He forced leading members of Rome's government to participate in religious rites celebrating this deity, presiding over them in person. According to the accounts of Cassius Dio and the Augusta, he married four women, including a Vestal Virgin, in addition to lavishing favours on male courtiers they suggested to have been his lovers, and prostituted himself. His behaviour estranged the Praetorian Guard, the Senate, and the common people alike. Amidst growing opposition, at just 18 years of age he was assassinated and replaced by his cousin Severus Alexander in March 222. The assassination plot against Elagabalus was devised by Julia Maesa and carried out by disaffected members of the Praetorian Guard.

Domitian (/dəˈmɪʃən, -iən/ də-MISH-ən, -⁠ee-ən; Latin: Domitianus; 24 October 51 – 18 September 96) was Roman emperor from 81 to 96. The son of Vespasian and the younger brother of Titus, his two predecessors on the throne, he was the last member of the Flavian dynasty. Described as "a ruthless but efficient autocrat", his authoritarian style of ruling put him at sharp odds with the Senate, whose powers he drastically curtailed.

Domitian had a minor and largely ceremonial role during the reigns of his father and brother. After the death of his brother, Domitian was declared emperor by the Praetorian Guard. His 15-year reign was the longest since Tiberius. As emperor, Domitian strengthened the economy by revaluing the Roman coinage, expanded the border defenses of the empire, and initiated a massive building program to restore the damaged city of Rome. Significant wars were fought in Britain, where his general Agricola made significant gains in his attempt to conquer Caledonia (Scotland), and in Dacia (Modern-day Romania), where Domitian was unable to achieve a decisive victory against King Decebalus. Domitian's government exhibited strong authoritarian characteristics. Religious, military, and cultural propaganda fostered a cult of personality, and by nominating himself as perpetual censor, he sought to control public and private morals.

Nerva (/ˈnɜːrvə/; born Marcus Cocceius Nerva; 8 November 30 – 27 January 98) was a Roman emperor from AD 96 to 98. Nerva became emperor when aged almost 66, after a lifetime of imperial service under Nero and the succeeding rulers of the Flavian dynasty. Under Nero, he was a member of the imperial entourage and played a vital part in exposing the Pisonian conspiracy of 65. Later, as a loyalist to the Flavians, he attained consulships in 71 and 90 during the reigns of Vespasian and Domitian, respectively. On 18 September 96, Domitian was assassinated in a palace conspiracy involving members of the Praetorian Guard and several of his freedmen. On the same day, Nerva was declared emperor by the Roman Senate. As the new ruler of the Roman Empire, he vowed to restore liberties which had been curtailed during the autocratic government of Domitian.

Nerva's brief reign was marred by financial difficulties and his inability to assert his authority over the Roman army. A revolt by the Praetorian Guard in October 97 essentially forced him to adopt an heir. After some deliberation Nerva adopted Trajan, a young and popular general, as his successor. After barely fifteen months in office, Nerva died of natural causes on 27 January 98. Upon his death he was succeeded and deified by Trajan. Although much of his life remains obscure, Nerva was considered a wise and moderate emperor by ancient historians. Nerva's greatest success was ensuring a peaceful transition of power after his death by selecting Trajan as his heir, thus founding the Nerva–Antonine dynasty. He was the first of the Five Good Emperors.

Nero Claudius Caesar Augustus Germanicus (/ˈnɪəroʊ/ NEER-oh; born Lucius Domitius Ahenobarbus; 15 December AD 37 – 9 June AD 68) was a Roman emperor and the final emperor of the Julio-Claudian dynasty, reigning from AD 54 until his death in AD 68.

Nero was born at Antium in AD 37, the son of Gnaeus Domitius Ahenobarbus and Agrippina the Younger (great-granddaughter of the emperor Augustus). Nero was three when his father died. By the time Nero turned eleven, his mother married Emperor Claudius, who then adopted Nero as his heir. Upon Claudius' death in AD 54, Nero ascended to the throne with the backing of the Praetorian Guard and the Senate. In the early years of his reign, Nero was advised and guided by his mother Agrippina, his tutor Seneca the Younger, and his praetorian prefect Sextus Afranius Burrus, but sought to rule independently and rid himself of restraining influences. The power struggle between Nero and his mother reached its climax when he orchestrated her murder. Roman sources also implicate Nero in the deaths of both his wife Claudia Octavia – supposedly so he could marry Poppaea Sabina – and his stepbrother Britannicus.

Sextus Afranius Burrus (born AD 1 in Vasio, Gallia Narbonensis; died AD 62) was a prefect of the Praetorian Guard and was, together with Seneca the Younger, an advisor to the Roman emperor Nero, making him a very powerful man in the early years of Nero's reign.

Agrippina the Younger chose him as Prefect in 51 to secure her son Nero's place as emperor after the death of Claudius. For the first eight years of Nero's rule, Burrus and Nero's former tutor Seneca helped maintain a stable government. Burrus acquiesced to Nero's murder of Agrippina the Younger but lost his influence over Nero anyway. He died in 62, some say from poison, though officially he died of throat cancer.