Seibertron was built millions of years ago by the Quintessons as a factory world. They installed the supercomputer Vector Sigma into its center prior to Seibertron's completion. When the factory went online, it began to produce two lines of robots- Consumer Goods and Military Hardware. Over time, the Quintessons endowed the robots with an artificial intelligence so that they could build themselves, but they treated the early Transformers as slaves, cruelly oppressing them. This led to the First Seibertronian War, which ended with Seibertron in the Transformers' possession.
Thus began the Golden Age of Seibertron, where the Transformers of both production lines developed culture and civilization. However, conflict arose between the former Consumer Goods- now Cybertrons- and the former Military Hardware- now Destrons. As the Second and Third Seibertronian War ravaged the planet, Seibertron's golden hue and vast stores of resources- not to mention huge chunks of the world's surface- were ruined and destroyed. With Seibertron in need of resources and embroiled in constant warfare, some Transformers left their homeworld to colonize other places, such as Paratron. When Earth was brought to the Transformers' attention in 1984, both sides tried to send resources back to their respective sides (using vastly different methods to get them, of course). At one point, the Destrons even went to the length of pulling Seibertron into Earth's orbit, in order to turn the human world into a rapidly crumbling source of massive power. (It was later returned to its normal location.)
In the race for resources and conquests, however, the Destrons were more successful, and ultimately conquered Seibertron by 2005. In 2005, Seibertron was shaken by the attack of Unicron, who destroyed the planet's twin moons and devastated the Destron forces, allowing the Cybertrons to take over. (Unicron's head became the new "moon" to replace the ones lost.) The Destrons were driven to Charr, but the Cybertrons' chance crash-landing on the planet Quintessa reminded the Quintessons of their lost factory world. Still stinging from their defeat, the Quintessons began their own efforts to conquer Seibertron in 2010, nearly succeeding on a few occasions before they were driven to deep space.
In 2011, the Headmasters became involved in the Cybertron-Destron war, and Vector Sigma began to show signs of instability. Convoy was able to correct Sigma and save Seibertron by sacificing his life (again). Later, Seibertron was destroyed by bombs planted in Vector Sigma by Megazarak, forcing Rodimus Convoy, Char and Blurr to search for a new Cybertron homeworld.