Patron saints associated with the military
The military saints, warrior saints and soldier saints are patron saints, martyrs and other saints associated with the military. They were originally composed of the early Christians who were soldiers in the Roman army during the persecution of Christians, especially the Diocletianic Persecution of AD 303–313.
Most of the early Christian military saints were soldiers of the Roman Empire who had become Christian and, after refusing to participate in Imperial cult rituals of loyalty to the Roman Emperor, were subjected to corporal punishment including torture and martyrdom. 
Veneration of these saints, most notably of Saint George, was reinforced in the Latin Church during the time of the Crusades. The title of "champion of Christ" ("athleta Christi") was originally used for these saints, but in the late medieval period also conferred on contemporary rulers by the Pope.
Since the Middle Ages, more saints have been added for various military-related patronages.
Hagiography.
In Late Antiquity, Christian writers of hagiography, prominently including Sulpicius Severus in his account of the heroic, military life of Martin of Tours, created a literary model that reflected the new spiritual, political, and social ideals of a post-Roman society. 
In a study of Anglo-Saxon soldier saints (Damon 2003), J. E. Damon has demonstrated the persistence of Sulpicius's literary model in the transformation of the pious, peaceful saints and willing martyrs of late antique hagiography to the Christian heroes of the early Middle Ages, who appealed to the newly converted societies led by professional warriors and who exemplified accommodation with and eventually active participation in holy wars that were considered just.
Iconography.
The Military Saints are characteristically depicted as soldiers in traditional Byzantine iconography from about the 10th century (Macedonian dynasty) and especially in Slavic Christianity. 
While early icons show the saints in "classicizing" or anachronistic attire, icons from the 11th and especially the 12th centuries, painted in the new style of ("imitating nature"), are an important source of knowledge on medieval Byzantine military equipment.
The angelic prototype of the Christian soldier-saint is the Archangel Michael, whose earliest known cultus began in the 5th century with a shrine at Monte Gargano.
The iconography of soldier-saints Theodore and George
as cavalrymen develops in the early medieval period.
The earliest image of St Theodore as a horseman (named in Latin) is from Vinica, North Macedonia and, if genuine, dates to the 6th or 7th century. Here, Theodore is not slaying a dragon, but holding a "draco" standard.
Three equestrian saints, Demetrius, Theodore and George, are depicted in the "Zoodochos Pigi" chapel in central Macedonia in Greece, in the prefecture of Kilkis, near the modern village of Kolchida, dated to the 9th or 10th century.
The "dragon-slaying" motif develops in the 10th century, especially iconography seen in the Cappadocian cave churches of Göreme, where frescoes of the 10th century show military saints on horseback confronting serpents with one, two or three heads.
In later medieval Byzantine iconography, the pair of horsemen is no longer identified as Theodore and George, but as George and Demetrius.
List.
Eastern Orthodox Church.
In the Romanian Orthodox Church:
The Russian Orthodox Church: 
References.
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