This well organized and concise article puts it all together:
Muhammad the Initiator of the Conquests
Muhammad the Trader
Muhammad the King
Muhammad the Monotheist Revivalist
Muhammad the Lawgiver
Muhammad the Prophet/False Prophet
The author, a major scholar in the field of Islamic studies, concludes by evaluating the utility of these sources: “Since the Muslim perception of Muhammad underwent major change during this period, this means that Christian sources can sometimes provide evidence for this change where Muslim sources are silent.”
See: “The Earliest Christian Writings on Muhammad: An Appraisal” by Robert Hoyland (2000)