Is the next Buddha the same entity/being as the previous Buddha, or another discrete being who comes to the same realizations as the previous Buddha?

I do not have a strong theoretical grasp of the concept of rebirth, so I am wondering: Is each Buddha that has existed/will exist the same being, reincarnated? Or is each Buddha a totally unrelated person from the previous Buddhas and Buddhas to come, who just happens to realize all of the same truths that the previous Buddha realized? Thank you