Born approximately in 570 CE in the Arabian city of Mecca, Muhammad was orphaned at an early age; he was raised under the care of his paternal uncle Abu Talib. After his childhood Muhammad primarily worked as a merchant. Occasionally he would retreat to a cave in the mountains for several nights of seclusion and prayer; later, at age 40, he reported at this spot, that he was visited by Gabriel and received his first revelation from God. Three years after this event Muhammad started preaching these revelations publicly, proclaiming that "God is One", that complete "surrender" (lit. islām) to Him is the only way (dīn) acceptable to God, and that he was a prophet and messenger of God, similar to other Islamic prophets.
The revelations (each known as Ayah, lit. "Sign [of God]"), which Muhammad reported receiving until his death, form the verses of the Quran, regarded by Muslims as the "Word of God" and around which the religion is based. Besides the Quran, Muhammad's teachings and practices (sunnah), found in the Hadith and sira literature, are also upheld by Muslims and used as sources of Islamic law (see Sharia).
At times Muhammad was indeed harsh to those in his power, but this was not out of keeping with the times. His marital relations: at his death he had nine wives and one concubine (a kept woman without marriage) must also be judged in the framework of the times. A political purpose can be traced in all of his marriages.
Once it was clear the Jews would not accept him, Muhammad began to minimize or eliminate the Jewish influence on his beliefs. For example, he shifted the direction of prayers from Jerusalem to Mecca, made Friday his special day of prayer, and renounced the Jewish dietary laws (except for the prohibition on eating pork). Originally, he said the Arabs were descendants of Abraham through his son Ishmael, but in the Koran Abraham's connection to the Jews is denied, with Muhammad asserting that Abraham is only the patriarch of Islam, not Judaism as well, because he "surrendered himself to Allah."
At Muhammad's death a division arose regarding his successor. Followers of Ali became known as Shia while followers of Abu Bakr became known as Sunni .