What is the name of the planet where the Transformers originate?

The planet where the Transformers originate is Cybertron.

Cybertron is the fictional homeworld of the Transformers, including both the heroic Autobots and the villainous Decepticons. It is usually portrayed as a vast metallic world filled with machine-built cities, energy networks, and ancient technology rather than oceans, forests, or ordinary geological terrain. Iacon is commonly depicted as its capital.

Different continuities explain Cybertron’s origin in different ways. In several G1-derived stories, the planet is linked to Primus, a godlike being whose planetary form became Cybertron. The AllSpark or the Well of AllSparks is also frequently associated with the creation of Cybertronian life, although its exact role changes between versions.

A common mix-up is confusing Cybertron with Earth, where many characters adopt vehicle disguises. In the original G1 setup, the Autobots and Decepticons leave Cybertron after a devastating civil war, crash on prehistoric Earth, and remain dormant for about four million years. Earth is therefore a major setting, but Cybertron is their origin world.