Muhammad was the Founder of Islam

Muhammad (peace be upon him) was born in Mecca in the year 570. Since his father died before his birth, and his mother shortly afterwards, he was raised by his uncle from the respected tribe of Quraysh. As he grew up, he became known for his truthfulness, generosity and sincerity, so that he was sought after for his ability to arbitrate in disputes.
The historians describe him as calm and meditative. Muhammad (peace be upon him) was of a deeply religious nature, and had long detested the decadence of his society. It became his habit to meditate from time to time in the Cave of Hira' near Mecca. At the age of 40, while engaged in a meditative retreat, Muhammad (peace be upon him) received his first revelation from God through the Angel Gabriel. This revelation, which continued for 23 years is known as the Quran. As soon as he began to recite the words he heard from Gabriel, and to preach the truth which God had revealed to him, he and his small group of followers suffered bitter persecution, which grew so fierce that in the year 622 God gave them the command to emigrate.
This event, the Hijra 'migration', in which they left Mecca for the city of Medina, marks the beginning of the Muslim calendar. After several years, the Prophet and his followers were able to return to Mecca, where they forgave their enemies and established Islam definitively. Before the Prophet (peace be upon him) died at the age of 63, the greater part of Arabia was Muslim, and within a century of his death Islam had spread to Spain in the West and as far East as China. He died with less than 5 possessions to his name.
While Muhammad (peace be upon him) was chosen to deliver the message, he is not considered the "founder" of Islam, since Quran tells us that Islam is the same divine guidance sent to all prophets before since Abraham (peace be upon him):


"Say: "Verily, my Lord hath guided me to a way that is straight,- a religion of right,- the path (trod) by Abraham the true in Faith, and he (certainly) joined not gods with Allah."[6:161].


"Say ye: "We believe in Allah, and the revelation given to us, and to Abraham, Isma'il, Isaac, Jacob, and the Tribes, and that given to Moses and Jesus, and that given to (all) prophets from their Lord: We make no difference between one and another of them: And we bow to Allah (in Islam)."[2:133].

Muslims believe all the prophets from Abraham, Jacob, Moses, Jesus etc. were all sent with divine guidance for their peoples. They were sent to their own people like Jesus said: "I was sent to the lost sheep of the children of Israel", but Muhammad (peace be upon him) was sent to all of mankind. Muhammad is the last and final messenger sent to deliver the message of Islam.
Muslims revere and honor him (peace be upon him) for all he went through and his dedication, but they do not worship him. "O Prophet, verily We have sent you as a witness and a bearer of glad tidings and a warner and as one who invites unto God by His leave and as an illuminating lamp."(Quran 33:45-6)