Millions of years ago, in a system many light-years from our own, the planet of CYBERTRON supported a life-force of mechanical, electronic creatures -- intelligent robots -- which could think and feel. As this race of robots advanced, they continued developing new technologies to increase their intelligence and abilities to incredible levels.
These robots had first been created 11 million years ago by a race known as the QUINTESSONS, who produced two lines of robots, household servants and military hardware, for sale around the galaxy. Their bodies were forged within the PLASMA ENERGY CHAMBER, a furnace deep within the heart of Cybertron that serves as a repository of plasma energy, a vast power capable of creating and destroying robotic life.
Contrary to the Quintessons' designs, the robots gradually gained self-awareness, and their leader, ALPHA TRION, eventually staged a revolution against the Quintessons, driving them off Cybertron, as the robots gained their freedom from their masters. The newly freed robots called themselves AUTOBOTS, short for autonomous robots, to designate their newfound independence. Peace reigned on Cybertron after the Quintesson revolution for a million years. But the line of military robots lusted for power and conquest. Calling themselves DECEPTICONS, the military robots tried to seize control of Cybertron for themselves, and war soon broke out all across Cybertron.
The peaceful Autobots, originally designed as household robots, knew they could never defeat the Decepticons with sheer firepower, so they turned to stealth and developed the art of transforming, with which they momentarily gained the edge. The Decepticons, however, quickly co-opted this technique as well. During this time, many Autobots left Cybertron to find peace elsewhere in the galaxy, and many Decepticons followed them through space, a time that would later be known as the SCATTERING.
On Cybertron, the Decepticons were united under the leadership of MEGATRON, the mightiest of the Decepticon warriors. They gained the upper hand for many years until Alpha Trion rebuilt a damaged Autobot factory worker, Orion Pax, into a new form, OPTIMUS PRIME, and passed to him the MATRIX OF LEADERSHIP, the repository of Autobot knowledge and the symbol of leadership. Optimus Prime was the Autobots' greatest leader, and he united the Autobots to fight back against the Decepticons.
The war raged as a stalemate for millions of years, and four million years ago, the planet Cybertron became completely depleted of ENERGON, the energy used by the Transformers, used up in the constant battles. Optimus Prime led a contingent of Autobots in an expedition to search for new sources of energy. Megatron followed and attacked Prime's ship, and both factions crashed into a volcano on the planet Earth.
They lay dormant for millions of years until they were reawakened in 1984, spurred on by renewed volcanic activity. They resumed their battles on Earth and on Cybertron. The Autobots, aided by human allies, defended the Earth against the evil Decepticons, who attempted to conquer it and steal its energy.
Shortly after the turn of the century, the Autobots helped humanity establish the EARTH DEFENSE COMMAND, an institution designed to protect Earth from additional alien attacks. With Autobot technology, humanity built space stations and fleets of starships to explore the galaxy and protect the world.
In 2005, the Decepticons made a final attack against Autobot City, the stronghold of the Autobots on Earth. Optimus Prime arrived and heroically saved the city from destruction, but was fatally wounded by Megatron in a final climactic battle. Megatron, himself damaged nearly beyond repair, was reformatted as the new robot GALVATRON by the giant planet-eater UNICRON. The Autobot Matrix in turn chose HOT ROD as the Autobots' new leader and reformed him into the Autobot commander RODIMUS PRIME. Rodimus led the Autobots to destroy Unicron and finally drive the last Decepticons off of Earth and Cybertron.
In 2006, Optimus Prime was rebuilt by a Quintesson when the entire galaxy was threatened by a plague that manifested itself by causing rampant, uncontrolled hatred in its victims. Rodimus returned the Matrix to Optimus after this incident, reverting back to Hot Rod, and Optimus resumed his command as leader of the Autobots.
In 2007, the Decepticons, now pariahs throughout the galaxy, staged one final attack against Optimus Prime, still stationed on Earth. The assault, known as the "Final Offensive," was devastating, resulting in the destruction of much of the EDC program and space stations in the solar system and many casualties in both the Autobot and human ranks. The Decepticons were finally driven back, but the resulting destruction was horrific on all sides. Captain MARISSA FAIREBORNE of the EDC, long a supporter of the Autobots, now argued that as long as the Autobots remained on Earth, they would forever invite attacks from Decepticons. As a result, Earth governments and the EDC passed a resolution that decreed that the Autobots must leave the Earth system. Before they left, however, the EDC developed the AUTOBOT DEFENSE PROTOCOL, which would give humanity a way to contact Cybertron for help if it ever needed it.
Since the departure of the last Autobot from the Earth system in 2007, there has been no contact between humanity and the Transformers for 20 years. True to Faireborne's belief, the Decepticons did not attack Earth once the Autobots had left. Humanity gradually rebuilt its EDC fleet and continued to explore the galaxy for the next 22 years, until it was suddenly dragged back into the Transformers' war by the events of 2029.
(Note: Stories of the Transformers traveling to the planet Nebulos and binary-bonding with its inhabitants have generally been dismissed as apocryphal.)