Espheni

The Espheni are the alien leaders in the series Falling Skies. They were previously called "Slenders" by fans.

Appearance
The Espheni are tall, thin, bipedal grey aliens. They tower over humans and Skitters. They look like dolphins from the chest up, leading the resistance fighters to call them "fish-heads." They have very skinny arms that go from their shoulders to their knees. Their eyes are mammalian in appearance and they do not appear to have noses, rather, two nostril-like holes around the corners of their eyes. While they prefer not to fight and direct their harness slaves to do the fighting, the Espheni are physically very strong. As demonstrated by the fact that an Overlord was seen effortlessly snapping the heavy metal chains meant to restrain him simply by standing up and swinging his arms. They carry concealable swords inside their arms and it is unknown what material it is made of.

In the Series
It is revealed near the end of the season 1 that the Overlords are the apparent masterminds behind the invasion of Earth in Falling Skies. They are first seen in Episode 8 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.

It is also known through examination of a Skitter corpse that the Skitters are also slaves due to the discovery of a harness buried in the corpse's spine. The resistance concludes that the Overlords use the Harness to generate the Skitters as a form of slave labor and then shock troops once the victim has been transformed.

In the series finale the Resistance is able to launch a powerful counterattack against the invaders. After discovering the 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 the structure 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 Karen; who 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 series.

At the start of the second series Tom is revealed to be one of many the aliens have "invited" aboard there ships. After enduring torture for 3 months 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. Tom disputes the overlords' claim that humanity is violent and savage contending that humanity's response is appropriate after the Espheni invaded earth and slaughtered much of humanity. Tom refuses the deal, and along with the other captives, is placed in front of a firing squad but somehow Tom survives.

They are later revealed to have invaded the Skitter home world 100 years prior to the invasion of earth where they ravaged the planet and enslaved the population. However in that time the some harnesses began to fail allowing some skitters to retain their free will although the Overlords took steps to ensure this never occurred in large enough numbers for effective resistance. By the time of the invasion of Earth  a small underground movement had arisen in the skitter ranks who became more active having been inspired by humanity's defiance in the face of invasion.

Fearful of their own slaves revolting the Overlords attempted to recapture Ben Mason who had been in contact with the revolt leader, Red Eye. Their plan to capture him nearly succeeds but is stopped by the arrival of the Second Mass who manage to capture an Overlord, who unbeknownst to them, operates all command staff in the east America.

After joining a Resistance movement, the Second Massachusetts and the Skitter Rebellion unite and launch an attack on an unknown Anti-Air Cannon. Inside, the Rebellion explains that the Overlords gather all their knowledge and strategies within not a computer net, but in a certain Overlord's mind who will be visiting a storage facility. Invading the facility, the 2nd Mass and the Rebellion are baffled when the weapon is not aimed at them but up at the sky.

After 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, the remaining members of the scattered Rebellion rescue them. During the turmoil of the battle, the leader of the Skitter Rebellion, Red Eye, dies and the Second Mass. avenges his death: by killing the Overlord.

In the aftermath of the battle, pod-like ships rain down from the sky and one lands near the 2nd Mass. Inside, a New Alien emerges and it is presumed that the Overlords tried to stop this race of beings from entering Earth.

Purpose
The aliens motive behind the unprovoked invasion is their own prophecy

Technology
The Overlords possess highly advanced, invasive, and destructive technology which they have employed in their invasion of Earth. Most aspects of their technology employs not only other alien species, but fuses an organic species with a form of inorganic machinery. This includes:
 * Airships: The Alien equivalent of Earth fighter jets used for transport and also bombing runs on the Resistance when they were still in the city.
 * Mechs: Robotic soldiers used to crush any resistance in the initial invasion and to hunt down any survivors after a foothold is established.
 * Harness: A truly invasive and horrifying device used by the aliens on abducted children. Initially used for mind control it eventually mutated the wearer into a Skitter, adding to the Overlords' forces.
 * Implants: These horrifying bugs are only an inch long and inflicted to a human when a Skitter or harnessed child puts it in the inflicted's eye. The implants cause the infected to develop a second personality that spies for the Espheni.
 * Crawlies: A blue spider-like creature that can infest bodies of animals (including humans) and use them like Trojan Horses. They then crawl out of their mouth and attempt to repeat that process.
 * Dragonflies: Small messenger drones that carry secure information from Implant spies to the Overlords.

Interactions with Humans
Initially the aliens held little regard for humanity; viewing them as vermin and ordering their forces to eradicate and enslave any survivors of their attack they came upon. They are disgusted by humans killing each other yet have no qualms with murdering another race to suit their needs. They initially had little concern for the human resistance; apparently confident in the fact their forces will deal with them soon enough.

When humanity's resistance efforts however prove to deal a significant blow to the alien forces they are intrigued. They send a representative and a human slave as a mouth piece to intercept Tom and Weaver and threaten reclaiming his son in return for him going with them to "Talk".