The theory of Buddhism is that a Buddha is a person who has worked towards perfecting all the Paramis over many lifetimes. When they actually perfect all Paramis, it's at a time when there is no other teachings of Enlightment, no other teachings of Buddhism at that time. They have totally disappeared from the world, okay? So - Sidhhartha Gotama who was our Buddha worked over many lifetimes. He discovered the deeper teachings, became fully enlightened and became a Buddha. Then as he taught and other people became fully enlightened, they were called Arahants.
Now he was the first person in our history, in our historical coverage of life as we know it. According to Buddhist teachings, though, is that aeons go by. Long, long periods of time. A Buddha rises, teaches, other people get enlightened and eventually the teaching disappears. Like for example today, there probably aren't many enlightened people, at least none that I've felt are fully enlightened. So slowly enlightened people disappear, then all lower levels of enlightened people disappear, then the teachings eventually disappear, and one day off in the future even the word "impermanence" won't be in our vocabulary. Wow, think of that one, will you?
It's like you will have everything you need to keep your body looking kind of permanent. Maybe every building will be built of some material that doesn't decay. It's a weird concept, but of course you can see it in normal life. You can see how people are going in that direction, you can see how somebody, some movie-star, eighty years old has had some cosmetic surgery and now they look like they are forty. You know, trying to be permanent.
And if you've ever read the book "Brave New World", you actually see that sort of concept in action as in prediction. The guy who wrote that was a Buddhist by the way.
So, according to the theory of Buddhism there are these cycles similar to the day coming up, the day going down, the next day coming around and around and around. Over very long periods of time. As much as we know our Buddha was one of about 26 Buddhas and that's counting back to when he made a vow to become a Buddha, which is called becoming a Boddhisatva. And way back when he did that, there was another Buddha alive at that time. That's kind of how they count things within Therevadin Buddhism.