the person who brang religion in Arabia was no one! Muslims (who believe the religion called Islam) believe that Allah (god) created the religion from the beginning of time which is also written down in their holy book called the quran.
In recent times Indian immigrants to Arabia have brought Hinduism with them and Filipino immigrants have brought Roman Catholicism with them. (While Christianity does have a historic presence in Arabia, Catholicism specifically never did.) However, prior to modern immigration, Arabia remained almost exclusively Muslim. (It is predominantly Sunni Muslim with Twelver Shiite Muslims along the northern Persian Gulf coast, Zaydi Shiite Muslim in northern Yemen, and Ibadi Muslims in Oman.)
There is no ruler of Islam, it is a religion. the head may be called a caliph.
The official (and only accepted) religion in Saudi Arabia is Islam. Therefore, the Qur'an is its holy book.
The main religion of Saudi Arabia is Islam
Islam spread from Arabia.
Saudi Arabia's primary religion (along with most of the Middle East) is Islam.
Saudi Arabia is known as the 'birth place' of a more specific religion, Islam.
The religion revealed by Muhammad - Islam.
Arabia is now called Saudi Arabia.
Many people believe that the religion of Islam was founded by the Prophet Muhammad (peace be upon him) in the land of Arabia. However, Muslims believe that all the prophet's brought the religion and message of Islam and hence there is no single one place where Islam was founded.
The vast majority of Saudi are Wahhabi Muslims. Being any religion other Muslim is illegal in Saudi Arabia.
It's a part of their religion and in Saudi Arabia every religion except Islam is banned by the law.