Embrico of Mainz
Embrico of Mainz was a twelfth-century scholar and the author of the Vita Mahumeti.
Embrico wrote the Vita in verse, modelled on the verse hagiography of contemporaries such as Hildebert of Le Mans. Whereas earlier texts had portrayed Islam as pagan idolatry and Muhammad as a pagan deity, Embrico and subsequent 12th century scholars viewed Islam as a form of Christian heresy and Muhammad as a particularly vile heresiarch.
Earlier studies of this change have explained it as a response to further exposure to Islam, though the resurgence of heresy within Christian Europe is of note.
In each case, Islam is associated with forms of doctrinal corruption: paganism for the early Middle Ages, heresy for the twelfth century.
See John Tolan, "Anti-Hagiography: Embrico of Mainz's Vita Mahumeti," Journal of Medieval History 22 (1996), 25-41.
___, Saracens: Islam in the Medieval European Imagination. New York: Columbia University Press, 2002.