The biography everyone knows, the prince kept from all knowledge of suffering, the four sights of an old man, a sick man, a corpse and an ascetic, the flight from the palace, is not in the earliest strata of the canon in that form. The oldest accounts are fragmentary and first-person, describing a young man of good family who saw that he was himself subject to ageing, sickness and death, and left. The full palace narrative is assembled in later biographical texts, reaching its most influential literary form in Ashvaghosha's Buddhacarita in perhaps the second century CE. The father who imprisons his son in pleasure, the departure at night, the charioteer: these are the tradition's own storytelling, and they are excellent, and they are not the earliest layer.
What is early and consistent is the shape of the teaching. He tried extreme asceticism, nearly starved, concluded that self-mortification does not work any better than indulgence, and formulated a middle way. The four noble truths state a problem, a cause, a cessation and a path, in the form of a medical diagnosis.
The most distinctive thing in the early material is what he declines to discuss. Asked whether the world is eternal, whether the soul is identical with the body, and what becomes of a liberated person after death, he sets the questions aside as not conducing to liberation, the undetermined questions. The parable of the man shot with an arrow, who refuses treatment until he knows who fired it and of what caste, is the canon's own account of why.
He was a teacher, not a god, and Buddhist traditions differ sharply on how far that remains true.