Sergius I of Constantinople

Sergius I of Constantinople, born in five hundred sixty-five, was a significant figure in the early Christian church, serving as the Ecumenical Patriarch from six hundred ten until his death in six hundred thirty-eight. His tenure was marked by his staunch support for Emperor Heraclius, whom he crowned in six hundred ten, and his involvement in the defense of Constantinople against the Avar-Persian-Slavic forces during their invasion in six hundred twenty-six.

Of Syrian Jacobite heritage, Sergius I was a pivotal proponent of Monothelitism, a theological stance that posited Christ's dual natures were united by a single will. This doctrine was articulated through the Ecthesis, a formula he presented in response to opposition from Chalcedonian supporters, including Maximus the Confessor and Sophronius of Jerusalem. The Ecthesis, which sought to suppress discussions on the nature of Christ's energies, was signed by Heraclius in six hundred thirty-eight, the same year Sergius I passed away.

Despite its initial acceptance, the Ecthesis faced significant challenges following the death of Pope Honorius I, leading to a decline in Monothelitism's support. Ultimately, the doctrine was condemned in six hundred forty by Pope John IV, and both Sergius I and Pope Honorius I were labeled heretics by the Third Council of Constantinople in six hundred eighty-one.