Isaakios, member of the military family Komnenos, had a long and successful career in the army before coming to power through a military coup, with the blessing of the powerful Patriarch Michael I Keroularios. Isaakios worked tirelessly; the pace and scope of his reforms aimed to cut waste and restore the empire to a firm financial and military footing. He was relentless in his collection of taxes due to the state, in cancelling alienations of state property, and in restricting monastic landholding. This last act brought emperor and patriarch into conflict, and Isaakios had Keroularios arrested in 1058. He deposed the patriarch, at whose trial Michael Psellos offered testimony, and installed in his place Constantine III Leichoudes. Isaakios was able to stave off Pecheneg attacks, and in 1059 formed a treaty with the Hungarians. Contracting a serious illness while hunting, he abdicated, choosing Constantine Doukas as his successor.
The reign of Isaakios marks a great (and scandalous) innovation on seals and coins: the representation of the emperor holding a drawn sword and wearing armor. There was no precedent for this direct reminder of the origins of Isaakios’s power; usurpers generally sought divine verification with the portrayal of a saintly coronation. On seals, this was the first use of military costume or paraphernalia since Tiberios III three-and-a-half centuries earlier, although Constantine IX holds a sheathed sword on his class 4 histamenon (1054/55) as well as on his miliaresion (1042–55). Isaakios’s seals are also the first imperial seals to have an inscription composed entirely of Greek characters. In addition, Isaakios is the first to employ his family name (Komnenos) on his seals, although Constantine IX added Monomachos to his two-thirds miliaresion. Isaakios maintained the image of Christ Emmanuel on the obverse of his seals.