In the earlier Theravada form of Buddhism prevalent in India in the centuries following the life of the Buddha, it was taught that there is only one Buddha for each era.
Therefore there are other Buddhas before and after Gautama Buddha, the historical.
It was taught that Buddhism, much like Hindu practices, would progress and then decline in each yuga or cosmic era. A single era could be millions of years long.
Whenever the Buddhist Dharma (teaching) in one yuga had declined to the point that it virtually no longer existed, a new Buddha would come into the world to renew the Dharma