Two persistent Western errors are worth clearing.
He is not worshipped. Islamic theology is emphatic that he is a man, that the sin the tradition treats as unforgivable is associating anything with God, and that veneration of the Prophet must not cross into it. The obsolete European term Mohammedan, which implied otherwise, was rejected by Muslims for exactly that reason. He is also not held to be the founder of a new religion in Islamic self-understanding: the claim is restoration, that Abraham, Moses and Jesus brought the same message and that it had been corrupted.
The title that carries the weight is seal of the prophets, from Quran 33:40, and the reading of it, that he is the last, that prophecy ends with him, is the point at which Islam draws its sharpest internal and external boundaries. The Ahmadiyya movement, founded in the nineteenth century, understands the seal differently and holds its founder to be a prophet in a subordinate sense; for this it is declared non-Muslim by state law in Pakistan and by most Sunni and Shia authorities, and its members face legal disability and violence.
The other great division is not about him but about what happened after. Sunni tradition accepts the succession of Abu Bakr, Umar, Uthman and Ali as rightly guided; Shia tradition holds that authority was designated to Ali and his descendants and that the community went wrong at once. That disagreement, about the sixty years after his death, has structured the religion for fourteen centuries.