A Buddha is a person who has developed all positive qualities and eliminated all negative qualities. A Buddha was an “ordinary” human like you and me before he/she became enlightened. Enlightenment is compared to awakening, as a person suddenly expereinces a complete transformation of body and mind from sleeping to waking up. One could say that a Buddha represents the very peak of evolution, as he/she is omniscient or all-knowing. 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.
The historical Buddha, Shakyamuni or Gautama Buddha, lived about 2,500 years ago in India. However, he was not the first Buddha, and will not be the last either. 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). Numbers one to three are Krakucchanda, Kanakamuni, Kashyapa, then comes Shakyamuni (the historical Buddha some 2,500 years ago), and the next Buddha will be called Maitreya. A Buddha is different from “God” in the Christian-Judeo-Islamic sense in that he/she is not the creator of the universe, is not omnipotent (all-powerful), and the state of Buddhahood can be reached by every living being (although it may take many lives). However, a Buddha is omniscient (knows everything) and can in that way be of tremendous help to other living beings.