John I Tzimiskes murdered Nikephoros II in 969, took the throne, destroyed the Rus' invasion of Bulgaria, and campaigned deep into Syria before dying in 976.
John Tzimiskes was an Armenian aristocrat of the Kourkouas family, a general of the first rank, and the nephew by marriage of Nikephoros II Phokas, under whom he fought at Aleppo in 962.
In December 969 he led the conspiracy that murdered Nikephoros in the palace, and took the throne himself. The patriarch made him do public penance and expel the empress Theophano before he would crown him, which he did.
What followed was one of the more effective short reigns in Byzantine history: the Rus' driven out of Bulgaria, eastern Bulgaria annexed, and Syrian campaigns that reached further south than any Byzantine army had gone in three centuries. He died in 976, probably of illness, possibly of poison.
He was born around 925 in the Byzantine east to an Armenian family connected to the Kourkouas clan, which had already produced John Kourkouas, the general who took Melitene in 934.
The nickname Tzimiskes is usually explained from an Armenian word for short stature, and the sources describe him as a small, fair, physically extraordinary man — an outstanding horseman and athlete, and personally brave to the point of recklessness.
He rose under Nikephoros Phokas, commanded in the eastern campaigns of the early 960s, and was one of the two generals who took Aleppo in 962. When Nikephoros became emperor, Tzimiskes became Domestic of the Schools of the East.
The sources are unusually consistent, and they are not flattering in a simple way. He was generous, charming, physically magnetic and popular with soldiers in a manner Nikephoros never managed — and he murdered a sleeping man to take his throne.
Leo the Deacon, who is broadly favourable, does not conceal the killing or the fact that it was squalid. Nor does the tradition conceal the penance: Polyeuctus refused him the crown until he had confessed publicly, named and exiled his accomplices, expelled Theophano, and repealed Nikephoros's laws against the church.
He accepted all of it, which tells you something. He wanted the throne enough to kill for it and enough to be humiliated for it, and having got it he governed with an energy and competence that made the manner of his accession an awkward footnote rather than the story.
His most dangerous inheritance was in Europe. Nikephoros had invited Sviatoslav of Kiev to attack Bulgaria as a proxy, and Sviatoslav had come, won, and decided to stay — with a Rus' army established on the Danube and no intention of going home.
Tzimiskes went north in 971, took the Bulgarian capital Preslav by storm, and pinned Sviatoslav in the fortress of Dorostolon on the Danube. The siege lasted three months and involved several savage engagements outside the walls, with the Byzantine fleet closing the river behind the Rus'.
Sviatoslav came to terms and withdrew, and was killed by Pechenegs on the way home. Tzimiskes annexed eastern Bulgaria outright — the Bulgarian patriarchate was abolished and the emperor Boris II was deposed in a ceremony in Constantinople — which solved a problem Byzantium had had for three centuries and created the one Basil II would spend his reign finishing.
In 974 and 975 he campaigned in the east with the army Nikephoros had built, and went further than the reconquest had yet reached: through Syria, taking Homs, Baalbek and Damascus into tributary status, and down toward the coast of Palestine.
Byzantine and later Latin writers made a great deal of how close he came to Jerusalem, and his own letter to the Armenian king Ashot III claims more than the campaign achieved. What he actually did was reduce a string of Syrian cities to tribute without holding them.
He died in January 976 shortly after returning, of an illness the sources describe with enough detail to suggest typhoid and enough suspicion to suggest poison — the chamberlain Basil Lekapenos, whose corruption Tzimiskes had begun investigating, being the usual candidate.
He held together everything Nikephoros had taken and added Bulgaria to it, and he handed the empire to Basil II in a condition that made the following half-century possible.
His accession remains the difficulty. The archive's account of Nikephoros's murder and of Antioch belongs to the same six weeks as the start of this reign, and the two men cannot be assessed apart: the best general of the generation killed the best general of the one before, and then governed better than anyone expected.
The Byzantine tradition's solution was the penance. It let the murder be atoned for and the reign be judged separately, which is a very Byzantine resolution to a problem of legitimacy and is more or less how history has treated him since.