Buddhism is an older religion then Christistanity. But we in the West often get information about Buddhism that is misinformed.
Elizaberth the Queen of England. It would not be polite to call her Queen. The late Pope John Paul. We would not say, Hay John come here. Hay Pope...

Buddha is a title. It means the enlighten one. It's not someones name. That why it is more polite to say The Buddha when speaking of Gautama Siddharta.
The Buddha's original name was Siddhartha. It meant one who had accomplished his aim. Gautama was Siddhartha's family name. Siddhartha was known all over the world as The Buddha, the Enlightened. He was also known by the name of Sakhya Muni, which meant an ascetic of the Sakhya tribe. Some of the problems with understand can be attributed to translation of one or several languages to English.
Buddhism, Thailand