The Espheni, also known as Overlords (males) and Queens(females), are an alien race and the apparent architects of the Invasion of Earth.
The Espheni became space-farers at some point in their species' existence, bringing them into conflict with other species in the universe. Experts in mechanical and biological engineering, they use harnesses to command humans and skitters – their enslaved subjects - and appear to have designed their own advancedweaponry. The first species to be attacked by the Espheni were the Dornia, whom they enslaved and mutated via harnesses into the first skitters. Despite their victory in the war, the Espheni developed a strong fear of the surviving members of the Dornia and left their own galaxy to collect as many resources to fight against them.
Their crusade led them to invade several worlds, including the Volm homeworld. The resulting conflict with the native Volm begun a centuries-long war where the Espheni were hunted by the Volm who committed their entire species to guerilla warfare against the Espheni.
In 2011, the Espheni returned to the planet Earth where they mounted an invasion of the planet, exterminating most of the human species. Months after the initial invasion, however, the Espheni became caught in a war as the remaining humans began organizing a resistance against the Espheni, refusing to be exterminated and in turn they had to face several new enemies such as Skitter rebels who were joined by their centuries-old enemies, the Volm and a few years afterwards, their ancient enemies, the Dornia. During a confrontation between resistance leader Tom Mason and the Espheni Queen in the ruins of the Lincoln Memorial, Tom Mason manages to infect the queen with the Dornia bioweapon, killing her. The death of the Espheni queen affects the entire race and they are wiped out.
It is thus that through the Espheni's conquering and enslaving ways, they foolishly created several mortal enemies for themselves over the centuries; the Dornia, the Volm, the race or races of the Skitter Rebellion, and Humanity. Once the races they'd attacked rallied together to fight back, the Espheni ended up fighting a losing war on several fronts, and ultimately caused their own demise.
The Espheni are originally from another galaxy.
At some point around 2,000 years ago, intergalactic Espheni explorers came across a unique habitable planet in a strategic location, Earth. In order to utilize its immense resources and strategic capability, the queen of the Espheni race ordered the Espheni to land on Earth.
A few hundred years later, the Espheni Queen sent a small invasion force to Earth led by her greatest warrior- her own daughter, landing in the land which would eventually be named South America and the Espheni came into contact with the local Nazca "primitives". The primitive humans managed to defeat the small invasion force and kill the queen's daughter and the other Espheni sent with her. Enraged at the death of her beloved daughter, the queen swore to one day return to Earth with a thousand times the force she sent last time and wipe out humanity in revenge. (Reborn)
Over 1,000 years ago, the Espheni came into conflict with the first race they would engage in large-scale warfare, a race known as the Dornia who were located within their own galaxy. Ultimately, the Espheni appeared to win the initial conflict, resulting in the enslavement of a large amount of the Dornia species and their conversion into the first Skitters via harnesses. The Dornia model would later serve as a blueprint for other enslaved species to become Skitters. The Espheni were then driven from their home galaxy by the surviving Dornia through a combination of biological warfare resulting in a large amount of fear of the Dornia arising amongst the Espheni, and as a result they were pushed into the Milky Way Galaxy, and would continue to be relentlessly pursued, forcing them to attack/conquer any world they came into contact with in order to gather resources to fuel their war machine.
As the Espheni continued to invade planets and enslave multiple species, they eventually came across a planetinhabited by the advanced Volm, proceeding to invade and conquer the planet in a short amount of time. The Volm then evacuated most of their race from the planet in time and engaged the Espheni in a drawn-out war across the galaxy. The Espheni traveled to many different planets in order to find and destroy their new enemies. The Volm pursued Espheni forces attempting to liberate conquered planets as revenge, eventually allowing them to end up at Earth again due to the two endless conflicts they fought.
It is revealed several months after the invasion that the Overlords are the apparent masterminds behind the invasion of Earth. They are first seen by Resistance fighters of the 2nd Mass Tom Mason, Hal Mason and Cpt. Dan Weaver on a scouting mission in the city. Tom believes that the aliens are only now showing themselves because they believe they are safe and have won.
In the season one finale the Resistance is able to launch a powerful counterattack against the invaders. After discovering that Skitters and Mechs are linked through a radio frequency, they come up with a jamming frequency that they use to disorientate and repel an attack on the Resistance base. This leads to a mass retreat by the alien forces back to their tower in the city. Tom believes that they have managed to confuse and possibly even scare the aliens. Taking advantage of the retreat, Tom is able to fire a missile at a fleeing ship that crashes into the alien structure, causing significant damage.
As Tom and Weaver are returning to the Resistance meeting point, they are confronted by former comrade Karenwho has been harnessed weeks ago. Approaching her cautiously Karen addresses Tom and says that the Overlords brought her here because they don't understand. An alien ship with an Overlord arrives and Karen explains that they did not anticipate such resistance from a less advanced race than their own. This has interested them and they now want to talk. Weaver and Tom are furious at this revelation that the aliens are only now acknowledging their victims when they fight back hard.
It is soon revealed that the aliens want specifically to speak with Tom, since his son is still under the influence of the Harness conversion process, due to it being removed too late. In exchange for going with the aliens Tom's son would be released from the process; with no other option Tom is forced to leave with the aliens, ending the first season.
At the start of the second season, Tom is revealed to be one of many the aliens have "invited" aboard their ships. After being detained for an unspecified length of time, Tom is brought before an Overlord to hear a proposition. Humans will be allowed to live in neutral zones in exchange for the surrender of the Resistance. Tom however sees this as nothing more than a prison camp, arguing with the aliens that their view of humanity as violent and savage is ironic when they attacked mankind in such a genocidal manner. Tom refuses to be relocated, and is released unarmed from the ship where a skitter and mech are waiting as a firing squad. Of the released captives, only Tom is allowed to survive by Red Eye, the rebel skitter's leader.
Red Eye soon reveals to the resistance that the Overlords invaded his homeworld 100 years prior to the invasion of earth where they ravaged the planet and enslaved the population, converting them into Skitters. However, in that time, some of the skitters had found a way to oppose the Overlord's control, rendering the harnesses useless. By the time of the Earth invasion a small resistance movement had arisen in the skitter ranks, who became more active after having been inspired by humanity's defiance in the face of extinction.
Fearful of their own slaves revolting, the Overlords attempted to recapture Ben Mason who had been in contact with the rebellion leader Red Eye. Their plan to capture him nearly succeeds, but is stopped by the arrival of the 2nd Mass., who manage to capture an Overlord. Unbeknownst to them, the Overlord is the sole military commander of the eastern half of North America.
The Second Massachusetts and the Skitter Rebellion unite and launch an attack on an unknown Espheni weapon site, where they know the Overlord will be. Invading the facility, the 2nd Mass is baffled when the weapon is aimed at the sky rather than at them, hinting at the arrival of the Volm.
Upon setting plastic explosives at the base of the facility, they are captured by a horde of Skitters and greeted by Karen. After being tortured by her, members of the Skitter Rebellion rescue them. Within the turmoil of the battle, the leader of the Skitter Rebellion attacks the Overlord and is killed. Their battle reveals the previosly unknown fact that the Overlords are either armed with a blade strapped to their wrist, or they possess a sharpened spike as part of their anatomy. As the Overlord is killing Red Eye, Tom grabs the staff used to torture them with and proceeds to engage the Overlord. The fight is very one sided, and is quickly over as Tom repeatedly smashes the Overlord's head. The strength of the Espheni species comes into question at this point, because the Overlord was capable of throwing Red Eye easily through the air, yet is unable to overpower Tom with a staff.
In the aftermath of the battle, pod-like ships rain down from the sky and one lands near the 2nd Mass. who are at this point back in Charleston. Inside, a new alien emerges and it is presumed that the Overlords tried to stop this race of beings from entering Earth.
After the Volm arrival, the Human Resistance, Skitter Rebellion, and the Volm destroy Espheni bases all along the Eastern coast of North America, liberating large swaths of land from them. To counter this, the Espheni place Karen in charge of all Espheni operations in the Eastern half of North America, replacing the previous Overlord. The Espheni also prepare to connect the Motherships across the world in a grid to slowly irradiate the planet, which would kill all non-harnessed life. Knowing that the Human Resistance and Volm will attempt to destroy a Mothership in one of four cities, they capture Tom and desperately try to extract the information from him, using hallucinations of a pre-invasion world to get him to reveal the location they plan to attack. However, Tom realizes what is going on and resists the dream.
After Tom escapes, the Volm and Human Resistance destroy the Boston Mothership with a Volm Weapon, taking out the grid and allowing a large Volm ship to land on Earth with reinforcements. The Espheni retreat to the Northern areas of the world, leaving most of the planet to the Volm and Humans.
The Espheni then attack the Volm refugees in the Alicante System of the Milky Way Galaxy, forcing most of the Volm to leave Earth to defend their race, leaving only a few recon teams on Earth. The Espheni then take back most of the planet, capturing human adults and placing them in ghetto camps across the globe. Large amounts of human children are seperated from adults and instead of being harnessed, are sent to re-education camps to be brainwashed into serving the Espheni.
The Espheni reveal their plans to mutate/skitterize Human adults into serving as a new front-line army against the great enemy that drove them from their home, who are approaching.
As of "Shoot the Moon", the Espheni have become incapacitated as a result of the deaths of The Monk and Scorch as well as the destruction of their power core, resulting in all Espheni Ghetto barriers coming down and Espheni technology being disabled, and causing many to flee. Among the chaos caused by this, their ancient pursuers have finally arrived in the Solar System.
Following the destruction of their power core, all mechanized Espheni technology has either gone offline or has a significantly reduced amount of energy, an example seen when several mega-mechs attempted to attack the 2nd Mass but only were able to power themselves for a few seconds. Espheni aircraft and spacecraft in the vicinity of Earth has also been affected, resulting in numerous beamers crashing to Earth and several Overlords fleeing Earth. The Espheni, however, continue to maintain control of large sections of the planet and have begun regrouping.
All ghettos have also run out of power, resulting in their walls coming down, in turn resulting in a mass exodus by many human prisoners and a limit to their goal of human skitterization, as both the stationary and portable mutation devices no longer are able to continue processing humans and fresh harnesses appear to no longer work.
One Overlord whose beamer crashed to Earth from space attempted to hide out in a nearby high school close to the 2nd Mass stronghold at Chinatown and began taking control of the skitters and hornets immediately surrounding the area, plotting to either protect himself or attack the 2nd Mass. Whatever his plans, the 2nd Mass were ultimately influenced by the Dornia who led them to his location, where Tom Mason killed him.
Another Overlord began plotting to use the already skitterized humans to attack the resistance groups and use any remaining Espheni power to reproduce hornets and skitters, but was stabbed and captured by Hal Mason. The 2nd Mass used techniques to get inside the Overlord's brain, and destroyed the hatchlings which were reproducing the skitters and hornets. Anthony later murdered it when it was trying to use the Shadow Plane to communicate with other Overlords.
Despite several setbacks, the Dornia's arrival and the greater success of the resistance has forced the Espheni to begin construction of a as-of-yet unknown weapon which could turn the war back in their favor, while the Dornia have begun constructing their own unknown weapon to supposedly render the Espheni extinct.
Following the destruction of the Espheni power station, the 2nd Mass has begun a march on Washington, DC to defeat the Espheni once and for all, collecting other militia groups along the way. Recently, through the Shadow Plane, Ben Mason discovered that the Overlords served previously-unknown Higher Beings. The Dornia reveal to Tom Mason that this being is actually the Espheni queen who only comes to a planet when victory is certain. They supply Tom Mason with a weapon that when used in the queen's presence, will wipe out the Espheni. Using information from the Shadow Plane, its later determined that the queen is at the Lincoln Memorial in Washington, DC.
After discovering that the Espheni have erected a powerful defensive wall around the city, Tom Mason decides that instead of an all-out attack on the Lincoln Memorial, they will launch a surgical strike to assassinate the queen. While the other militias assault the wall directly and create a distraction, Tom and Colonel Weaver lead a small team to the Lincoln Memorial through the city's service tunnels. Tom is eventually separated from his team, but reaches the Lincoln Memorial alone. In the ruins of the Memorial, Tom and the Espheni queen come face to face and the queen explains the Espheni's history with Earth and why she wants humanity destroyed. When the queen starts draining his blood, Tom infects himself with the Dornia bioweapon. The virus passes through his blood into the queen, killing her. With the queen's death, all the other Espheni start dying and explode into ashes one by one, rendering the race extinct and freeing the Earth from their rule.