Empress Pulcheria (399(ish)–453) was the daughter of Emperor Arcadius, who died when she was nine and her brother Theodosius, the heir, was seven. When her regent disappeared mysteriously, Pulcheria, 16, was declared Augusta in her own right, and took over the regency. At this point (or just before), she and her sisters took a vow of virginity, in part out of religious feeling, but also as a huge favor to their brother—no little royal nephews padding about meant less chance of a knife in the dark.
Officially Pulcheria “co-ruled” with her brother, although in reality she was his mentor and guide. Even after assuming power, Theo never really got the hang of it. Pulcheria once demonstrated this by handing him an order for her own death, which he signed without reading it. “Oops,” he said upon being shown his error. After that he mended his ways and became a model emperor. Hahaha! I had you going there, didn’t I? No, he never became a strong or capable ruler. He failed to codify Roman law, lost important battles, and suffered the doubling of the tribute to the Huns.
Knowing what’s really important, though, he asked Pulcheria to find him the most beautiful woman in the world, all other considerations be darned. She found Eudochia, a schemer (and heretic) who, in cahoots with the eunuch Chrysaphius (who nevertheless had the—um—fortitude to oppose the empress), exiled Pulcheria, but this was later reversed when Eudochia exerted herself one time too many, and found herself exiled.
In 431, Theodosius called the (Ecumenical) Council of Ephesus to rule on the nature of Christ. Nestorius had demoted the Theotokos to Christotokos by dividing the natures of Christ in such a way that Mary was the mother of Christ, but “Christ” here doesn’t mean the preincarnate Logos, which was not and could not be united to human nature in the way that . . . . Well, it’s complicated. At any rate the council ruled against Nestorius, but so great was his power with Theo that a second council, the so-called “robber council” of 449, was called, which overturned Ephesus. Pulcheria, an ardent Theotokian, opposed Nestorius vociferously, and he struck back by accusing her of (among other things) sexual inconstancy (with seven(!) men). A cry and hue arose from Patriarch Cyril of Alexandria and Pope Leo I, among others, who affirmed the Theotokosity of the Theotokos and the honor of Pulcheria.
In 450 Theodosius died (kids, don’t take a header off your horse if you like living), resulting in a brief power struggle, resulting in Pulcheria’s empressification and Chrysaphius’ death under transparent circumstances. A woman emperor-in-her-own-right was beyond the empire’s (or at least the court’s) ability to accept, so she was compelled to marry. She chose Marcius, a powerful general who agreed to honor her vow of chastity, and who became a competent emperor in his own right. Together they called the (Ecumenical) Council of Chalcedon, which overturned the robber council and deposed Nestorius. (It also did other stuff, of course.) Pulcheria was thereafter highly praised by Cyril, Leo, and others, which is only proper, as I’m sure you’ll agree.
The Empress founded three churches in Constantinople dedicated to the Theotokos, and many hospitals, hospices, and things like that. She also effected the return of St. John Chrysostom’s remains to Constantinople (after his shameful exile (in which state he died) under her father (er, mother)). Pulcheria’s death was greeted with sincere dismay by her subjects (really). Her will specified that her remaining riches be given to the poor. She is the patroness, understandably enough, “against in-law problems.”