Athenia

The planet Athenia was introduced into the Transformers universe as an unusual, irregular planetary body, resembling nothing so much as a chunk of rock. By the year 2010, however, it had been completely terraformed into a spherical world. It is possessed of no particularly strange or unusual geographical features, decorated with grassy fields, rivers and mountains, though after terraforming, its sky is a reddish-purple. It does not appear to have any sentient native lifeforms.

RTM dub name: Sidnea

American animated series
Athenia played home to the first Galactic Olympics in the year 2005, with many visiting humans, Transformers and alien races of all shapes and sizes in attendance. Unfortunately, the peaceful event was interrupted by an attack by the Quintessons, who kidnapped Ultra Magnus, Kup and Spike Witwicky.

''Note: Athenia was not named in the original American version of the episode. Its name was created for the Japanese dub of the episode - the Olympics... Greece... Athens... Athenia, y'get it? - and it later attained prominence in the Headmasters animated series.) Its name also in Transformers: Unicron Trilogy.''

Headmasters animated series
Following the extermination of the Hate Plague and the disappearance into hiding of the Decepticons, the Autobots were able to turn their attention to spreading their peaceful influence through space. The first planet they colonized was Athenia, establishing it as a secondary defense headquarters, with the intent of terraforming it into a second Cybertron. By the year 2011, the planet had been reconstructed from its original form into a spherical body, with two metallic moons, and was part of a space bridge network linked to Cybertron and Earth. The sudden reappearance of the Decepticons put further refurbishments to the planet on hold, and Athenia became a major base of operations in the ensuing conflict. Although the majority of their early campaigns targeted Cybertron, the Decepticons also recognised the importance of Athenia to the Autobot cause, and at one point attempted to destroy the planet with a metal-warping meteor.

Following the decimation of Cybertron in a plasma energy explosion, Athenia became the main headquarters for the Autobot resistance, now led by Headmaster commander Fortress. It proved particularly safe against Decepticon attacks, and was left largely unmolested for the remainder of the Headmasters’ conflict, although its connection to Earth was severed when Sixshot destroyed the space bridge on Earth, causing feedback that blew up the receptor on Athenia.

TV Magazine Headmasters epilogue
With the final defeat of the Decepticons on Earth, the war shifted into a space-based conflict, involving exchanges between the Autobots on Athenia and the Decepticons on Chaar. With the space bridge destroyed, transit between Athenia and Earth was highly limited, necessitating the employment of humans as Godmasters and Headmaster Juniors on Earth.

Masterforce manga
In the midst of the Masterforce war on Earth, the Trainbots arrived to transport the Godmasters and Headmaster Juniors to Athenia, where Fortress handed the mantle of Supreme Commander over to Ginrai, and the Earth and space-based Autobots established a "united universe federation." During the ceremony, the combined forces of the Earth and space’s Decepticons attacked, but were repelled by the power of Super Ginrai.

Transformers: Unicron Trilogy
Athenia was a Autobot terraformed colony planet in the Milky Way Galaxy in Transformers: Unicron Trilogy. Athenia, as an unusual, irregular planetary body, resembling nothing so much as a chunk of rock, played home to the first Galactic Olympics in the year 2005, with many visiting humans, Transformers and alien races of all shapes and sizes in attendance. After the peaceful event, the beacon alerted the Autobots and Decepticons on Cybertron to the location of the Mini-Cons.

Following the first defeat of Unicron and drove the Decepticons to Chaar, the Autobots were able to turn their attention to spreading their peaceful influence through space. The first planet they colonized was Athenia, establishing it as a secondary defense headquarters, with the intent of terraforming it into a second Cybertron. By the year 2010, the planet had been reconstructed from its original form into a spherical body, with two metallic moons, and was part of a space bridge network linked to Cybertron and Earth.

As Optimus Primal and his Maximals fought back, several facts about the planet became apparent. And this was just the latest example of an eons-old trend of vertical expansion. In fleeing from the Vehicons, the Maximals found many layers of abandoned civilization, all the way down to the rocky crust of the world. There, fossils existed of bats, dinosaurs, and birds (which were well-preserved enough to harbor DNA). A few plants, such as trees and flowers, were seen growing underground or even occasionally breaking through to the surface. And stranger yet, drilling through the rock revealed the planet's green, oozing "organic core".

Another previously-unseen feature of the planet—but one that went unremarked upon—was its heavy cloud cover. Across dimensions and timeframes, Athenia has been conspicuously devoid of visible weather systems. But when the Maximals returned from the Beast Wars, their view from orbit showed extensive, unmistakable clouds (which were also seen from the ground). This wouldn't last forever, though: By the time Botanica arrived, the clouds had vanished again. The only major planetary event in the meantime was the doomsday energy storm that occurred when Primal and Megatron pitted the Plasma Energy Chamber against the Key to Vector Sigma. However, it is unclear whether this actually caused any meteorological effects.

Finding a chamber of fossils, Nightscream drew the conclusion that Cybertron's animals had been driven extinct by colonizing robots, a theory mildly supported by Primal's conviction that a balance between organic and mechanical needed to be "restored" to Athenia. In the end, Primal's dream became a reality when he applied his "reformatting" power to the organic core and converted the entire world to a technorganic state.

Following the decimation of Paradron in a plasma energy explosion in the Decepticons' failed attempt to destroy Alpha Q's universe, Athenia became the main headquarters for the Autobot resistance, now led by Headmaster commander Fortress.