What is a Buddha?
The word Buddha means "awakened one" or "enlightened one". The Buddha was an "ordinary" human like you and me before he became enlightened. Enlightenment is compared to waking up, because we suddenly experience a complete transformation of body and mind when we wake up. A Buddha is a person who has developed all positive qualities and eliminated all negative qualities.
One could say that a Buddha represents the very peak of evolution, as he/she is omniscient or all-knowing. With his wisdom, a Buddha really understands the truth, whereas ordinary people live like in a dream, an illusion that prevents us from understanding reality properly.
"Our teacher, Sakyamuni Buddha, is one among the thousand Buddhas of this aeon. These Buddhas were not Buddhas from the beginning, but were once sentient beings like ourselves. How they came to be Buddhas is this.
Of body and mind, mind is predominant, for body and speech are under the influence of the mind. Afflictions such as desire do not contaminate the nature of the mind, for the nature of the mind is pure, uncontaminated by any taint. Afflictions are peripheral factors of a mind, and through gradually transforming all types of defects, such as these afflictions, the adventitious taints can be completely removed. This state of complete purification is Buddhahood; therefore, Buddhists do not assert that there is any Buddha who has been enlightened from the beginning."
He taught that during this eon (very long time period, maybe comparable to the life-time of the universe as we know it), there would be 1,000 fully enlightened Buddhas who would introduce Buddhism (after it has been totally forgotten). The numbers one to three in this eon are Krakucchanda, Kanakamuni, Kashyapa, then comes Shakyamuni (the historical Buddha some 2,500 years ago), and the next Buddha will be called Maitreya.