Styled as a letter "H", the Helios moonbase is a massive space station that was built after the events of Borderlands. After its completion, Handsome Jack moved Helios to orbit above Pandora's moon Elpis. During Borderlands 2, Handsome Jack spends much of his time on Helios, conversing with the Vault Hunters through ECHO. In any outdoor location, Helios can be seen in the sky.
Helios is capable of launching orbital assaults known as moonshot blitzes which are capable of devastating the target areas, and can also send a ground assault almost anywhere by launching loaders and constructors. Its most powerful weapon is "The Eye of Helios", a massive laser consisting of multiple smaller lasers to destroy almost any landscape where it is fired at. It is powered by the eye of The Destroyer, the creature that was released and killed during the opening of the original Vault.
Supplies may be called in from Helios. Hyperion ground forces set up a supply beacon at a drop site to requisition said supplies, and the supplies are delivered in cargo containers in the same manner as the blitzes. The supply beacons can be used to requisition everything from equipment to Fast Travel stations. Although the latter will first have to be calibrated by the moonbase staff before they can function, they will immediately become operational once they land Two known supply drop sites include the Orbital Delivery Zone in Opportunity and the Extraction Plant at The Highlands - Outwash.
This station hints at the god of the Sun in Greek mythology. Hyperion is also his father.
In Borderlands: The Pre-Sequel, Helios is still under construction but is functional. Jack, then a programmer for Hyperion, is put in charge of supervising the construction, but Helios is invaded by the rogue Lost Legion led by Colonel Zarpedon and he is forced to evacuate for the time being. As Zarpedon begins using the Eye of Helios to destroy Elpis, Jack gathers a team of Vault Hunters and a robot army to retake Helios.
Helios is fully completed by the events of Borderlands 2. In the time since the first Vault on Pandora was opened, Hyperion had been fighting the Crimson Raiders led by Roland for control of the planet. The Raiders' headquarters was located in the city of Sanctuary, which had to be reinforced with a shield generator to protect it from moonshot blitzes from Helios. The generator draws its energy from power cores that burn out periodically, requiring replacements that force the Raiders to venture from the safety of the city to seek. During the mission The Road to Sanctuary, the Vault Hunters deliver a new power core for Sanctuary's shield generator just before Helios launches another blitz, sparing the city from what would have been a devastating attack.
Later, when the Vault Hunters defeat Wilhelm, they retrieve a unique power core from his remains that could theoretically sustain Sanctuary's shields indefinitely. When installed in the generator in Rising Action, however, the core is revealed to be a Trojan horse that allows Angel to infiltrate and disable the shield's systems, rendering Sanctuary defenseless. Helios then begins a heavy bombardment of the city, killing many of its inhabitants before Lilith uses her powers to phase the city to the Highlands and out of the moonbase's range.
During Bright Lights, Flying City, Angel attacks Helios when the technicians on board delay establishing a Fast Travel link with a terminal the Vault Hunters deploy in Overlook. In order to expedite the Fast Travel request, Angel deactivates the life support as a death threat, which shortens the time for the request from three to six weeks to a few minutes.
During Tiny Tina's Assault on Dragon Keep, Brick, Lilith, and Mordecai play a game of "Bunkers & Badasses" with Tiny Tina while the six other Vault Hunters "interrogate" a Hyperion spy for Helios's access codes. After the game is finished, Maya informs the group that the spy has finally divulged the codes and asks if they feel like blowing the moonbase up.
After the events of Borderlands 2 and the DLCs, in Tales from the Borderlands, Helios is still up and functional after the death of Handsome Jack and his mining operations on Pandora. It sent several moonshots to the planet's surface which includes Rhys, Vaughn in a car and a Loader Bot shortly after.