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.
(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.)
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 colonised 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.
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.