From Seven Myths of the Spanish Conquest, by Matthew Restall (Oxford, 2004), Kindle Loc. 511-524:
Cortés emerged in the sixteenth century as the most recognizable of God’s agents for several reasons. One was the impressive nature of the Mexica empire and the subsequent importance of central Mexico to the Spanish empire. Another was the rapid publication and wide circulation (despite royal attempts at censorship) of Cortés’s letters to the king, which argued unambiguously that God had directed the Conquest of Mexico as a favor to the Spanish monarchy. The blessed status of Cortés himself was heavily implied; in one letter he uses the Spanish term medio (medium or agent), to describe his providential role. A third was the supportive spin placed on Cortés and the Conquest by the Franciscans.
Friars of the Order of St. Francis were the first Spanish priests into the Mesoamerican regions that would become the colonies of New Spain. In competition with the Dominicans, to a lesser extent other orders, and later the secular clergy (priests who were not members of an order), the Franciscans remained central to the activities of the church throughout colonial Spanish America. In central Mexico, Yucatan, and other parts of New Spain, sixteenth-century Franciscans were the driving force behind efforts to convert native peoples and build a colonial church. The roles that natives themselves played in that process, and the writings generated as a result by both friars and natives, gave rise to an extraordinary body of literature that was foundational to the academic discipline of ethnography.
The Franciscans saw Cortés’s support of their entry into Mexico and their activities in the earliest colonial years as being crucial to their mission, and as a result contributed much to the formation of his legend.