Gaius Pius Esuvius Tetricus was a Gallo-Roman nobleman who ruled as emperor of the Gallic Empire from 271 to 274 AD. He was originally the praeses (provincial governor) of Gallia Aquitania and became emperor after the murder of Emperor Victorinus in 271, with the support of Victorinus's mother, Victoria. During his reign, he faced external pressure from Germanic raiders, who pillaged the eastern and northern parts of his empire, and the Roman Empire, from which the Gallic Empire had seceded. He also faced increasing internal pressure, which led him to declare his son, Tetricus II, caesar in 273 and possibly co-emperor in 274, although this is debated. The Roman emperor Aurelian invaded in 273 or 274, leading to the Battle of Châlons, at which Tetricus surrendered. Whether this capitulation was the result of a secret agreement between Tetricus and Aurelian or that surrender was necessary after his defeat is debated. Aurelian spared Tetricus, and made him a senator and the corrector (governor) of Lucania et Bruttium. Tetricus died of natural causes a few years after 274.

The primary sources for the Gallic Empire are substandard. According to numismatist Jerome Mairat, the most reliable contemporary sources of the Gallic Empire, are Aurelius Victor and Eutropius, although they are brief and believed to rely upon the hypothetical lost Enmannsche Kaisergeschichte. Historians Nicholson and Casey second this, describing a key source of information as being "brief notices by late 4th-century Latin authors who depended for much of their information on the lost Kaisergeschichte (Enmann's History of the Emperors)". Mairat states that Zosimus and Zonaras both reveal key information regarding the Gallic Empire in short sentences, relying upon the mostly lost works of Dexippus; Nicholson and Casey state more specifically that another main source for Tetricus, in particular, is "scattered allusions" from Zomimus' first book. Nicholson and Casey further posit another source as being "information gleaned from the rather copious coinage minted by the Gallic emperors". Lastly, Mairat states that the imperial biographies of the semi-fictional Historia Augusta provide a wealth of details regarding the Gallic Empire, with Tetricus being listed as one of the "Thirty Tyrants" within; however, this work is generally unreliable, with Nicholson and Casey stating that it the biographies "interweave fact, invention, and an idiosyncratic sense of humour." For instance, the Historia Augusta states that Tetricus was recognized in Hispania, but modern historians have rejected this.

According to historian John F. Drinkwater, Victor and Eutropius, who form the traditionalist view, cast Tetricus as being a "civilian" rather than a "soldier-emperor", therefore arguing he was not prepared to rule during a time of emergency, explaining why he was originally posted to Gallic Aquitania during his time as governor, rather than the Rhine. Eutropius states that Tetricus had to suppress rebellion when he first became emperor, which Mairat identifies with the usurper Domitian II, noting that Zosimus provides only that he rose to power at the beginning of Aurelian's reign, without providing the area of his rule, but that two coins minted in his name that have been discovered were doubtlessly made in the Gallic mints between 269-274, with the specifics of the coin suggesting a dating of c. mid 271. Mairat then suggests that Domitian's usurpation may have been an uprising of the army, based in the same areas as the mint, against Tetricus due to his civilian origin. However, Drinkwater argues the possibility that this "civilian" tradition is influenced by Emperor Aurelian's propaganda and notes that Victoria put forth significant funds to see him made emperor to secure her own position and that Aquitania was a significant province, bordered on all sides by areas (Gallia Narbonensis and Hispania) which were threatened, or had recently been re-conquered by Rome. Drinkwater goes on to state that such a position "must have required considerable ability, both administrative and military", arguing that he proved himself an able commander against the Germans, and concluding that "The last Gallic emperor should not be dismissed as a lightweight".

Epigraphic sources also provide some information: however, the epigraphic habit (the use of monumental inscriptions for public display) of the Roman Empire was in decline during the period, and many are undated. Fourteen inscriptions bearing Tetricus' name have been found in Gaul, although these are broken into two regions by a vertical line of inscriptions bearing Aurelian's name, which were made after the surrender of Tetricus; no Tetrican inscriptions overlap with Aurelianic inscriptions. There are another five inscriptions bearing his name that have been discovered in Britannia.

The Gallic Empire was a state composed of the Roman provinces which made up Britannia, Hispania, Gaul, and Roman Germania, which broke away from the Roman Empire during the reign of Emperor Gallienus. Gallienus had become emperor after his father, Emperor Valerian, was captured by the Sassanids in 260. Gallienus's rule occurred during the Crisis of the Third Century (235–284), a period of intense political and military power struggles. Gallienus was overwhelmed by numerous issues, including several usurpers, as well as attacks in the Balkans and along the Rhine by various tribes. Hispania was also impacted, with raids from the Franks, with historian Lukas De Blois describing the raids against Hispania Baetica as "grievous", and the city of Tarraco (modern-day Tarragona) being sacked in the 260s, As a result of the threat to the empire, certain governors were appointed as dux (leader) of an entire border line, including Postumus in 258-259. Because Gallienus was unable to prevent the raids, Postumus rose up and declared himself emperor; at about the same time, he assassinated Saloninus, Gallenius's son and co-emperor, in Colonia (modern-day Cologne). Postumus focused on defending the Gallic Empire, and, in the words of the 4th-century Roman historian Eutropius, "restored the almost exhausted provinces through his enormous vigour and moderation."

Gallienus attempted to invade the Gallic Empire twice, in 260 and 265, but was repulsed both times, forcing him to accept the secession. Although he was unable to conquer the Gallic Empire, Gallienus did ensure that the Roman Empire was defended; he stationed Aureolus, a military commander, in northern Italia, to prevent Postumus from crossing the Alps. Postumus was killed by his soldiers in 269 in Mogontiacum (modern-day Mainz) while putting down a revolt by the usurper Laelianus, because he would not permit them to sack the city. After the army killed Postumus, they elected Marcus Aurelius Marius, an officer, as Gallic emperor. While some Roman historians, such as the 4th-century historians Aurelius Victor and Eutropius, hold that Marius reigned for only two days before being killed by Victorinus, who had served as praetorian prefect (commander of his praetorian guard) under Postumus, the number of coins issued by Marius indicate that he must have served for a longer time, a period of roughly three months. Victorinus declared himself emperor in mid-269 in Augusta Treverorum (modern-day Trier), two days after killing Marius. Victorinus's rule was recognized by the provinces of Britannia and Gaul, but not by those of Hispania.

Gaius Pius Esuvius Tetricus, commonly referred to as Tetricus I, was born in Gaul, on an unknown date, to a noble family of Gallic origin. Little of his early life is known, however, he had become a senator and occupied the post of praeses provinciae (provincial governor) of Gallia Aquitania, a province in the southwest of what is now France, by 271. In early 271, emperor Victorinus was murdered in Colonia by Attitianus, an officer in the Gallic army, allegedly because he had seduced Attitianus's wife. Because the motivation for his assassination was personal, rather than political, Victorinus's mother, Victoria, was able to retain power within the empire; as Drinkwater notes, she was unable to take the throne herself as a woman, and thus selected Tetricus as a candidate, having him appointed by the army after securing their support with large bribes; he further mentions the possibility that Tetricus was related to Victoria and Victorinus, but states that there is no direct support for this. The army proclaimed Tetricus as Gallic emperor in spring of the same year at Burdigala (modern-day Bordeaux). However, Tetricus was not present for the proclamation.

Drinkwater posits that, as he was governor of Gallia Aquitania, Victoria likely reigned for several weeks from Colonia before Tetricus assumed power, possibly issuing coins deifying Victorinus during this period. Mairat argues that, if Tetricus was absent for the proclamation, it is most likely that Victoria did order the minting of the coins, but notes that the coins of Domitian II appear to have been made in the same issue, noting that the coinage may have been created by the Gallic armies, due to political uncertainty regarding succession, or that Victoria may have minted coins in Victorinus' name, rather than Tetricus', for the same reason.