Majorian (Latin: Iulius Valerius Maiorianus; c. 420 – 7 August 461) was Western Roman emperor from 457 to 461. A prominent commander in the Western military, Majorian deposed Avitus in 457 with the aid of his ally Ricimer at the Battle of Placentia. Possessing little more than Italy and Dalmatia, as well as some territory in Hispania and northern Gaul, Majorian campaigned vigorously for three years against the Empire's enemies. In 461, he was murdered at Dertona in a conspiracy, and his successors until the fall of the Empire in 476 were puppets either of barbarian generals or the Eastern Roman court.

After defeating a Vandal attack on Italy in 457, Majorian intercepted the Visigoths in the Battle of Arelate, defeating them and saving the city. Securing Septimania, he reduced the Goths to federate status, returning Hispania to the empire. Meanwhile, Marcellinus was convinced to recognise Majorian, reconquering Sicily in the emperor's name. Majorian then attacked the Burgundians, reconquering Lugdunum and expelling them from the Rhône valley. Marching into Gaul, he reintegrated the Gallo-Romans and appointed Aegidius commander of the region, whilst Nepotianus invaded the Kingdom of the Suebi and reconquered Scalabis. In 460, Majorian entered Hispania and readied a fleet for an invasion of Africa. However, the Vandals bribed traitors into defection and destroyed the fleet in the Battle of Cartagena, forcing Majorian to return to Italy.

During his reign, Majorian instituted reforms to reduce corruption, rebuild the state's institutions and preserve ancient monuments. This led to an antagonistic relationship with the Roman Senate, which was exploited by Ricimer to behead Majorian upon his arrival in Italy in 461. The 6th-century writer Procopius asserted that Majorian "surpassed in every virtue all who have ever been emperors of the Romans", whilst Sidonius Apollinaris, a contemporary of the emperor, stated, "That he was gentle to his subjects; that he was terrible to his enemies; and that he excelled in every virtue, all his predecessors who had reigned over the Romans."

The life of Majorian and his reign are better known than those of the other Western Emperors of the same period. The most important sources are the chronicles that cover the second half of the 5th century—those of Hydatius and Marcellinus Comes, as well as the fragments of Priscus and John of Antioch.

Besides these sources, which are useful also for the biographies of the other emperors, some peculiar sources are available that make Majorian's life known in some detail, both before and after his rise to the throne. The Gallo-Roman aristocrat and poet Sidonius Apollinaris was an acquaintance of the Emperor and composed a panegyric that is the major source for Majorian's life up to 459. As regards his policy, twelve of his laws have been preserved: the so-called Novellae Maioriani were included in the Breviary of Alaric, compiled for Alaric II in 506, which helps to understand the problems that pressed Majorian's government.

Majorian was probably born after 420, as in 458 he was described as a iuvenis ('young man'). He belonged to the military aristocracy of the Roman Empire. His grandfather of the same name reached the rank of magister militum under Emperor Theodosius I and, as commander-in-chief of the Illyrian army, was present at his coronation at Sirmium in 379. The magister militum's daughter then married an officer, probably called Domninus, who administered the finances of Aetius, the most powerful general of the West. The couple gave the name Maiorianus to their child in honour of his influential grandfather, as was the custom for the firstborn son.

It was under the same Aetius that Majorian started his military career. He followed Aetius to Gallia, where he met two officers also under Aetius's command who were to play an important role in Majorian's life: the Suebic-Visigoth Ricimer and the Gallo-Roman Aegidius. Majorian distinguished himself in the defence of the city of Turonensis (modern Tours) and in a battle near Vicus Helena (447 or 448) against the Franks under Chlodio. In the latter, Majorian fought at the head of his cavalry on a bridge, while Aetius controlled the roads leading to the battlefield:

There was a narrow passage at the junction of two ways, and a road crossed both the village of Helena... and the river. [Aëtius] was posted at the cross-roads while Majorian warred as a mounted man close to the bridge itself...