There are many sutras that document the past lives of the Buddha, the most famous being the Jataka Tales, which are stories often told to children. The Jataka Tales are quite interesting in that if you read them to a child, no one would know it was about Buddhism. They appear to center more around tales of love and compassion, involving people and various animals like monkies.
I found this interesting video with a Norwegian monk named Ajahn Brahmali, who is staying in Western Australia. He goes over some of the past lives of the Buddha. He is trying to give people a better picture of who the Buddha was. His logic is that by knowing the Buddha’s past lives, one can get a better idea of who the Buddha was and how he got to where he is. He also talks about things like karma, understanding the cycle of existence, and the important messages that the Buddha talked about.
He explains things from the perspective of the Therevadin tradition and the Pali suttas.