Buddha refers to Siddhartha Gautama, the founder of Buddhism, who attained enlightenment and became known as 'the Awakened One.' His teachings emphasize the Four Noble Truths and the Eightfold Path as a means to overcome suffering and achieve Nirvana. The concept of Buddha plays a significant role in comparing Buddhism with Christianity and other major world religions, particularly regarding ideas of enlightenment, salvation, and the nature of existence.