Page "Cybertron" Paragraph 51

According to Transformers: The Movie Prequel comic book by IDW Publishing, Optimus Prime and Megatron co-ruled Cybertron.

The Allspark is responsible for giving life to the Transformers.

When Megatron begins a war to control it for himself, Optimus sends it into the depths of outer space in the hope that he can defeat him quickly.

The war drags on, and Optimus sends Bumblebee to retrieve it, because its absence will cause the planet to shut down.

It would later be revealed in the third film that Sentinel Prime was the Autobot leader when the war began and was seemingly killed as he attempted to flee Cyberton with a super weapon.

Optimus then took over full command, with the rest of the events likely playing out the same way.