Christian theologian in the context of "Cyril and Methodius"

Cyril (Greek: Κύριλλος, romanized: Kýrillos; born Constantine, 826–869) and Methodius (Μεθόδιος, Methódios; born Michael, 815–885) were brothers, Byzantine Christian theologians and missionaries. For their work evangelizing the Slavs, they are known as the "Apostles to the Slavs".

They are credited with devising the Glagolitic alphabet, the first alphabet used to transcribe Old Church Slavonic. After their deaths, their pupils continued their missionary work among other Slavs. Both brothers are venerated in the Eastern Orthodox Church as saints with the title of "equal-to-apostles". In 1880, Pope Leo XIII introduced their feast into the calendar of the Roman Rite of the Catholic Church. In 1980, the first Slav pope, Pope John Paul II declared them co-patron saints of Europe, together with Benedict of Nursia.

Nestorius of Constantinople (/ˌnɛsˈtɔːriəs/; Ancient Greek: Νεστόριος; c. 386 – c. 451) was an early Christian prelate who served as Archbishop of Constantinople from 10 April 428 to 11 July 431. He was a Christian theologian from the Catechetical School of Antioch, and several of his teachings in the fields of Christology and Mariology were seen as controversial and heretical, causing major disputes. In 431, he was condemned and deposed from his see by the Council of Ephesus, presided over by his archrival Cyril of Alexandria, but the counter-council led by John I of Antioch vindicated him and deposed Cyril in return. Nestorius refrained from attending both of these councils and instead sought retirement from the Byzantine Emperor.

Nestorius himself used the title Theotokos and did not advocate for its ban. His teachings included cautious usage of Theotokos ("God-Bearer"), used for Mary, mother of Jesus, in order that Christ's human and divine natures not be confused, as he believed Christ was born according to his humanity and not his divinity, which indicated his preference for the concept of the prosopic union of two natures (divine and human) of Christ, over the concept of a hypostatic union. He proposed instead the title of Christotokos ("Christ-bearer"). This brought him into conflict with Cyril of Alexandria and other prominent diophysite and miaphysite churchmen of the time, who accused him of heresy.

Theodore of Mopsuestia (Greek: Θεοδώρος, c. 350 – 428) was a Christian theologian, and Bishop of Mopsuestia (as Theodore II) from 392 to 428 AD. He is also known as Theodore of Antioch, from the place of his birth and presbyterate. He is the best known representative of the middle Antioch School of hermeneutics.

Huldrych or Ulrich Zwingli (1 January 1484 – 11 October 1531) was a Swiss Christian theologian, musician, and leader of the Reformation in Switzerland. Born during a time of emerging Swiss patriotism and increasing criticism of the Swiss mercenary system, he attended the University of Vienna and the University of Basel, a scholarly center of Renaissance humanism. He continued his studies while he served as a pastor in Glarus and later in Einsiedeln, where he was influenced by the writings of Erasmus. During his tenures at Basel and Einsiedeln, Zwingli began to familiarize himself with many criticisms Christian institutions were facing regarding their reform guidance and garnered scripture which aimed to address such criticisms.

In 1519, Zwingli became the Leutpriester (people's priest) of the Grossmünster in Zurich where he began to preach ideas on reform of the Catholic Church. In his first public controversy in 1522, he attacked the custom of fasting during Lent. In his publications, he noted corruption in the ecclesiastical hierarchy, promoted clerical marriage, and attacked the use of images in places of worship. Among his most notable contributions to the Reformation was his expository preaching, starting in 1519, through the Gospel of Matthew, before eventually using Biblical exegesis to go through the entire New Testament, a radical departure from the Catholic mass. In 1525, he introduced a new communion liturgy to replace the Mass. He also clashed with the Anabaptists, which resulted in their persecution. Historians have debated whether or not he turned Zurich into a theocracy.

Tatian of Adiabene, or Tatian the Syrian or Tatian the Assyrian, (/ˈteɪʃən, -iən/; Latin: Tatianus; Ancient Greek: Τατιανός; Classical Syriac: ܛܛܝܢܘܣ; c. 120 – c. 180 AD) was an Assyrian Christian writer and theologian of the 2nd century.

Tatian's most influential work is the Diatessaron, a Biblical paraphrase, or "harmony", of the four gospels that became the standard text of the four gospels in the Syriac-speaking churches until the 5th-century, after which it gave way to the four separate gospels in the Peshitta version.

Dale C. Allison Jr. (born November 25, 1955) is an American historian and Christian theologian. His areas of expertise include the historical Jesus, the Gospel of Matthew, Second Temple Jewish literature, and the history of the interpretation and reception of the Bible.

Since 2013, Allison is the Richard J. Dearborn Professor of New Testament at Princeton Theological Seminary. He was previously the Erret M. Grable Professor of New Testament at Pittsburgh Theological Seminary (1997-2013). From 2001-2014, he was an editor for the multi-volume Encyclopedia of the Bible and Its Reception.