Back in their home planet of Cybertron the Autobots (good guys) could transform into futuristic vehicles while the Decepticons (bad guys) could transform into flying machines; a few odd Autobot/Decepticon models could turn into other devices (gigantic microscopes, audio boom boxes, animals, etc.) but for the most part they were clearly only cars or planes. Energon, the fuel that kept all Cybertron inhabitants functioning, is in short supply and both robot clans are in a war (started by the Decepticons' desire to rid Cybertron of Autobots) that forces Autobots to look to other galaxies for alternate sources of energy. Then a ship full of both Autobots/Decepticons (they were doing battle onboard an Autobot space ship that the Decepticons boarded) crashed on Earth and encrusted itself into a volcano for millions of years. Did I mention all of these took place millions of years ago in a galaxy far, far away?
Anywho, in modern time the volcano where the space ship crashed erupted and re-activated the Autobots' computer, Teletran 1, which re-built both Autobots and Decepticons based on schematics of vehicles/planes of the time (1984) it could monitor from a surveillance satellite it launched into space whe it was re-activated. Had Teletran 1 not been damaged when the ship crashed against the volcano it would have never rebuilt the Decepticons first, thus ensuring the war between Autobots and Decepticons that raged in Cybertron would continue here on Earth.
Did I mention all of these takes place in the first six minutes of the first episode of the original "The Transformers" cartoon from 1984?