The well-rehearsed beginnings of Prester John ground the legend in rumor, hope, and prophecy. As Vsevolod Slessarev has shown, the legend can be traced to the earliest written accounts describing an Indian Christian visiting medieval Europe. Two Latin texts, both describing an event taking place in 1122, give an account of a certain “Patriarch John,” hailing from India, who travels to the Pope early that year. Both texts (the anonymous De adventu and a letter from Odo of Rheims) give an account of the vast wealth and power of Christians who guarded the shrine of St. Thomas.

Although these early twelfth century texts create the expectation of a powerful eastern Christian king, it is with Otto of Friesing that the legend truly begins. Inspired by civil unrest in Germany and written shortly after the fall of Edessa in 1144, Otto’s Historia de duabus civitatibus (1146) furnishes an anecdote a colleague had recently heard about a Nestorian Christian prince, Iohannes. 

Otto describes this figure as a morally pure, militaristically capable Eastern (Nestorian) Christian king claiming descent from the Magi. This Iohannes had recently conquered Persia and headed West to assist crusaders in their defense of the Holy Land. Unfortunately, Otto relates, a flooded Tigris River prevented him from aiding his Latin Christian brethren.

In addition to expanding the account offered by the two earlier twelfth-century texts, Otto's account corroborates a tradition of Eastern Christian potentates echoed in early medieval texts like the Historia Ecclesiastica of Eusebius of Caesarea. Although the anecdote Otto records spawned the centuries-long belief in an Eastern potentate capable of uniting Christendom, the initial account of an Eastern anti-Islamic leader was later revealed to refer to the deeds of the Qara Khitai, a nomadic Chinese tribe descending from Manchuria.

This early account of the legend can be viewed as a reflection of the era that produced it: unstable leadership (four popes in the decade), the ascendancy of the Cistercians, the first Latin translation of the Qur'an (1143), the fall of Edessa (1144), the unsuccessful Second Crusade that resulted therefrom (1145).

The cultural context surrounding Otto's text reflects much of this. After all, Otto was also uncle to Frederick Barbarossa, the emperor (1150-90) who, at the time of Prester John’s advent, was engaged in a power struggle with Pope Alexander III (1159-81). In 1160, Frederick chose to recognize "antipope" Victor IV over Alexander III; as a result, Alexander excommunicated the Emperor. 

The crusading support Prester John voiced likely helped assuage fears that the West might require outside assistance in order to maintain the recovered sites of Christian history.