- Constantine I the Great (306-337) is considered the first Byzantine emperor. Not all historians agree on that. Several sources view Theodosius the Great (379-395) as the first emperor, other his son Arcadius and some Heraklios (610-641).
- Constantine I was the first Roman emperor to rule from Constantinople. He was also the first Christian Roman emperor. He was baptized a little before his death.
- Eutropius who served under emperor Arcadius (395-408) was the first eunuch to become Roman Consul.
- Valens (364-378) was the first emperor who was killed in a battle. He disappeared in Adrianople fighting against the Visigoths.
- The characteristic baubles pendilia and kitch accessories which hung from the Emperors' crowns began with Marcian (450-457). Although the years saw the styles of crown change, the pendilia remained, at least through Manuel II Palaiologos(1391-1425).
- Marcian was also the first emperor crowned by the patriarch of Constantinople. He initiated a custom that was to be followed by all emperors after him. This practice gave to the patriarchs (and later to the popes who imposed it for all western rulers) immense political power
- Leo I the Thracian (457-474) created the force of the Excubitores, aka the palace guard. Many future emperors would take the position of comes excubitores (chief of the guard) and seized power taking advantage of their position
- Zeno (474-475 & 476-491) -nicknamed "the Barbarian"- was an Isaurian and the first "barbarian" (a person outside of the Greek-Roman educated elite) on the throne of Constantinople.
- The first violent regime change in Constantinople since its foundation was the coup d’ etat of Phocas against Maurice (602). Maurice was also the first emperor who was executed by his successor (Phocas was the second).
- Phocas (602-610) was the first emperor who used blinding and mutilation against his opponents. It became a common practice in the imperial affairs thereafter.
- The first mutilated emperor was Heraclonas (son of Heraklios). This practice was supposed to make the disfigured person ineligible to rule. Mutilation usually meant nose slitting (like in Heraklonas case) or tongue slitting (like in his mother’s case) or cutting off a limb or blinding.
- Phocas (602-610) was the first emperor with a beard. It is believed that he did that to hide a scar or his ugliness. Prior to this time, the emperors were clean shaven in the classical Roman fashion, except for those who affected the Greek "philosopher's beard," like Julian (361-363). After Phocas, the beard became a tradition and all adult emperors after him were bearded
- Phocas -again- was the first emperor crowned in a church, starting another permanent fixture in Byzantine ceremony (and in Western coronation ceremonials, in general).
- Heraklios (610-641) was the first to assume the Greek title "βασιλεύς" (king) instead of Caesar. He also made Greek the official language of the Eastern Empire replacing Latin.
- Constans II (641-668) who remained in history as Constantine Pogonatos launched the division of the Empire in themes (territories). A brilliant initiative which remained at the core of the Byzantine state organization until the end.
- The first effective use of the secret weapon of the Byzantines, the "Greek Fire", was made during the siege of the Constantinople by the Arabs (674-678), in the reign of Constantine IV (668-685) and it was the main reason that the Arabian fleet was defeated then. An earlier form of Greek Fire was also used during the rebellion of Valentinian, in 645.
- Justinian II (685-695 & 705-711) was the first emperor to place the image of Christ on his coinage (along with the motto Servus Christi).
- After his first deposition, Justinian II was exiled in Cherson. He escaped and sought refugee in the Khazar kingdom. There, he married the sister of the khan who took the hellenized name Theodora. When Justinian II came back to the throne, Theodora was the first foreigner who became empress of Byzantium
- Leo III the Isaurian (717-741) started Iconoclasm. Leo was a good Christian and an excellent emperor but Iconoclasm was a really bad idea.
- Irene of Athens (797-802) was the first female empress of Byzantium. She joined the royal family with her marriage to Leo IV. She may have also been the first instance of an imperial bride chosen through a beauty contest, a curious Byzantine custom enacted some five times between the late eighth and early tenth century.
- Irene of Athens (797-802) was also the first pure Greek on the throne. Although most of the Byzantine emperors were of a mixed Greco-Roman origin, Irene was an Athenian and apparently Greek. Her family name was "Sarantapichiotissa" which indicates that she came from a family of remarkably tall people.
- Constantine VI the Blind (780-797) was the first emperor who was blinded after his dethronement. Interestingly, many others followed. Another interesting thing in Constantine VI’s case is that he was blinded on his mother’s, Irini, orders!
- The first Byzantine emperor to have a family surname was Michael I Rhangabe (811-813).
- The first political marriage between the Byzantine state and Western Europe occurred in the time of John I Tzimiskes (969-976), who sent princess Theophano (sister of Basil II) to marry Holy Roman Emperor Otho II. After the death of her husband, Theophano was the acting ruler of the German Empire for 6 years.
- Alexander (912-913) was the first Byzantine emperor to use the term "autocrator" (αυτοκράτωρ, meaning "emperor") on coinage, to celebrate the ending of his thirty-three years as co-emperor. The "auto" could imply "alone on the throne, at last", but most probably the motive for the adoption of the title was that it had been used by another king with the same name: Alexander the Great.
- Isaac I Komnenos (1057-1059) was the first Byzantine emperor to use the double-headed eagle as a symbol of imperial power. Isaac was influenced from tales about this mythical creature (the haga) in his native Paphlagonia in Asia Minor. Its origin is traced back to the civilization of the Hittites.
In Byzantine heraldry, the two heads represent the dual sovereignty of the Emperor (secular and religious) and/or dominance of the Byzantine Emperors over both East and West.
Starting from Byzantium, the double-headed eagle became one of the most powerful heraldic symbols, since it is currently depicted in the flags of 3 countries and at least in 10 army flags around the world.
- John V Palaiologos (1341-1391) was the first emperor who visited a foreign country. Of course, other emperors had been abroad before but only in military campaigns. John V visited Venice on a diplomatic mission. Not a successful trip though. He was arrested there for bad debts.
- Constantine XI Palaiologos (1449-1453) was the first emperor who claimed the title "King of the Greeks". He was also the last...