According to the Greek philosopher Plato, "There will be no end to the troubles of states, or indeed of humanity itself, until philosophers become kings in this world, or until those we now call kings and rulers really and truly become philosophers." While Marcus Aurelius could indeed be considered Rome's first "philosopher King" (followed only perhaps by Julian), the irony is that his otherwise often considered exemplary reign also included a nearly constant state of war along the Danubian frontier.
Unfortunately, written ancient material on Marcus Aurelius is scattered among several sources or of dubious quality. Much like the history of his immediate predecessors, the history of Cassius Dio for this period is very fragmentary. The account in the Historia Augusta is extant but long debated for its accuracy and even the origin of its authorship. Later writings of Christian authors Tertullian, Eusebius and Orosius do provide additional and important information (though perhaps biased from a perspective of Christian persecution and martyrdom) along with the correspondence of Marcus' teacher Fronto. Of course, the emperor's own work "Meditations" provides intricate detail into the philosophy of the man but is less useful as a history of events.
Marcus Aurelius (originally Marcus Annius Catilius Severus) was born in Rome on April 26, AD 121 into a distinguished and wealthy family originating from Hispania. His great grandfather, Marcus Annius Verus was the first in the family to gain a Senate seat while also reaching the office of praetor. His grandfather was much revered by the Flavians (Vespasian, Titus and Domitian) and had been enrolled as a Patrician in addition to serving a rare three consulships. His father, also Marcus Annius Verus, died young when the future emperor was only about 3 years old leaving the young Marcus to be raised by his esteemed grandfather. His paternal aunt Annia Galeria Faustina (Faustina the Elder) was the wife of Antoninus Pius (and eventually Marcus' mother-in-law as well) and this familial connection certainly played a role in his eventual adoption by Pius. On his mother's side (Domitia Lucilla) Aurelius was related to other men of consular rank such as Catilius Severus (maternal great grandfather and hence his birth name) and Calvisius Tullus (maternal grandfather).
Though the nature of affiliation between the young Marcus and Hadrian is unknown, it is clear that Hadrian took an early interest in the boy's education. The emperor enrolled Marcus as an equestrian as early as his 6th year, made him a Salian priest at the age of eight and saw to his advanced education. Marcus was apparently so devoted to academic pursuits and his demeanor so serious and honest that Hadrian affectionately dubbed him 'Verissimus' meaning most truthful (which was later dropped with his "coming of age" around 15 years old and changed to Verus). His tutors were among the finest of the day and included Euphorion for literature, Geminus for drama, Andron for geometry, Alexander of Cotiaeum for Greek grammar, Trosius Aper, Pollio, and Eutychius Proculus of Sicca in Latin, Aninius Macer, Caninius Celer and Herodes Atticus in Greek oratory and Cornelius Fronto for Latin. Many honors were later bestowed upon these teachers, some with political office and others with wealth depending upon their social station. Perhaps a more important influence on Marcus Aurelius than these essentials of a Roman education, which also included such subjects as rhetoric and law, was the study of stoic philosophy. He became a dedicated student of the arts, learning directly from Apollonius of Chalcedon, and through the writings and lessons of men such as Aelius Aristides and especially Epictetus. His most in depth personal instruction seems to have come from one Junius Rusticus, who remained a trusted confidant of Marcus Aurelius as both teacher and imperial advisor.
Based on his education alone Marcus was clearly marked for imperial service of some sort by Hadrian, and this was reaffirmed when Hadrian named his first heir to the empire in AD 136. Marcus was previously engaged to the daughter (Ceonia Fabia) of this heir, one Lucius Ceionius Commodus, and certainly by no coincidence the young man was firmly entrenched as a member of the extended imperial family. However, the surprise passing of Commodus in January, AD 138 did little to supplant Marcus as an advancing political commodity. Hadrian was forced to find a new heir and turned to T. Aurelius Fulvus Boionius Arrius Antoninus, later simply Antoninus Pius. As a prerequisite to his promotion, he adopted both the 17 year old Marcus and the 8 year old son of the recently passed heir, also named Lucius Ceionius Commodus (later to be known simply as Lucius Verus after his adoption into the family of his co-heir Marcus). It was upon this adoption to Antoninus Pius that Marcus Annius Verus officially took the name Marcus Aurelius as an adopted member of the Antonine family.
During the reign of Antoninus, Marcus Aurelius continued his educational preparation for the imperial throne. While the pursuit of stoicism continued, his duties under the peaceful 23 year reign of Antoninus included regular advancement through the political cursus honorum, but was surprisingly devoid of military experience (this particular exclusion could have been a tragic oversight considering the political power of the army, but the eventual succession went about completely unopposed). To further cement his bond to Antoninus Pius, the engagement to Ceonia Fabia was broken off and Marcus was married to his cousin Faustina the Younger (the emperor's daughter) in AD 145. She eventually bore him 13 children, most of whom died young, including a daughter Lucilla (the future wife of co emperor Lucius Verus, and son Commodus the eventual heir to the throne and the emperor often associated with the beginning of the imperial decline.