Tom Mason (Noah Wyle)

Before the invasion, Tom was a history teacher, who lived in Cambridge, Massachusetts, after suffering the death of his wife and the capture of his son Ben, Tom joins the resistance movement with the 2nd Mass.
Despite that his knowledge of the war, and military history are just academic, Tom was appointed second in command of the 2nd Mass with the military commander, Daniel Weaver. Tom quickly proves to be a strong leader and his relationship with Dr. Anne Glass begins to turn into something special. Tom is determined to find and rescue Ben from captivity, and protect Hal and Matt, her other two children. At the end of the first season, makes contact with the leaders of the invasion. In the second season returns with the 2nd Mass, but some of them don’t trust him having conflicts with some of the members of the 2nd, especially with Pope. In the third season, having reached the village of Charlestone, Tom was appointed president of the new United States of America.

Anne Glass (Moon Bloodgood)

Before the invasion she was pediatrician, but after the attack, quickly takes the role of the doctor of the 2nd Mass.
She has lost her only son in the initial attack, a tragedy that can not be easily overcome, however, she uses her work to help with the current situation. This, along with his personality, generous and fighter, made her one of the pillars of the 2nd Mass. Her uncle and aunt, also found refuge in the resistance. She is a close friend of Tom, easily, as both believe in civil rights. Their relationship eventually becomes romantic when at the end of the first season Tom takes the first step, to share a first kiss, in front the imminent danger. In the second season, she begins a relationship with Tom, she has even got pregnant. During the third season, Anne cares for Alexis, daughter of Tom and her, but things do not go as they should and Anne escapes being captured by Karen.

Hal Mason (Drew Roy)

Hal is the older brother of the Mason brothers. Before the invasion, Hal was a popular athletic boy destined for success.
As a member of the 2nd Mass, becomes an important resistance fighter with only 17 years. After his brother Ben was captured and he saw how he should protect Matt, his younger brother, Hal shows how much his family means to him and how he would be able to do anything for them. During the first season, he has a relationship with Karen Nadler (until she is captured). After this event, and little by little, he is creating a special bond with Maggie, who becomes a relationship in the second season, after being attacked by Karen. At the end of the second season, in the mission of the 2nd Mass to destroy the weapon that the Overlords were building, is arrested along with the rest of the fighters, at one point in the battle Karen kissed him and left him unconscious. In the third season is discovered that Karen got implant a probe in his cerebral cortex, making it a possible mole within Charlestone, but they get stop it, and remove the parasite. His relationship with Maggie is stronger than ever.

Ben Mason (Connor Jessup)
Ben is the second son of Tom. Before the invasion, Ben spent most of his time reading and studying. But at the beginning of the first season, with the age of 14, he is a prisoner of the aliens.
He is rescued and since then, the camp refugees see him as a freak, as he still has the spikes on his bac, which makes Ben has “special powers”, is able to capture radio waves which the skitters use to communicate, have more strength, reflexes, speed and endurance. During the second season, he joins the rebellion of the skitters, becoming a key player in the battle against the Overlords. In the third season decides to stay with his family in Charlestone, continues fighting next  the skitters rebels and other children but also with humans and Volm in Charlestone.

Matt Mason (Maxim Knight)
He is the youngest son of Tom. At the age of eight years, in the first season has to face to some things that none of his brothers had to face at his age.
Her character evolves throughout the seasons, and although at first his greatest wish was to return to normal, he slowly was changing that idea into helping, becoming a soldier. This causes the start of the third season, he is a rebel who does not go to school. However, when things get more serious and tricky, often are Matt’s ideas which save the day. In this season he has to face events that affect him significantly. The link grows stronger with Anne, calling her “Mom”.

Lourdes Delgado (Seychelle Gabriel)

Lourdes is a devout Christian, her faith is even stronger after the invasion. Before the invasion, she was a young university, thus becomes the assistant of Dr. Anne Glass.
During the first season she looks to be attracted to Hal Mason, but in the second season, Lourdes has a relationship with Jamil. Whom dies, causing a loss of faith in her, but Anne helps her to return being herself,  even braver. In the third season, Lourdes is more mature, able to take over the hospital of Charlestone after maternity leave of Anne, but she hides a big and dangerous secret, which is the cause of a large number of deaths. During a scene it can see how the face of Lourdes is full of bugs, which ends to confirm that she is the mole, this explains her behavior. After getting stop her in chapter 9 of the third season, Lourdes falls into a state of madness. Alexis (daughter of Tom and Anne) will eliminate her internal bugs, supposedly saving her.

Anthony (Mpho Koahu)
Anthony is one of the best soldiers of the 2nd Mass. Before the invasion, Anthony had been a policeman in the city of Boston, so it is an excellent shooter and he volunteers for any battle without hesitation, even for the most dangerous missions . Although his has always been seen as a very valuable piece of the 2nd Mass, it is in Charlestone when his character gets more important, being in charge of the investigating about who’s the mole.

Margaret | Maggie | (Sarah Sanguin Carter)

Before the invasion, she had a difficult life, having cancer at a very young age and once when it had passed, she became a rebel on the run from everything, even having a son in prison, one that she has never seen again.
In the first season, she presented as part of Pope’s gang, then we know that she was raped, and after helping the 2nd Mass escape from Pope (and catch him), she joins them, becoming a great soldier. Strong, tough and fearless. She has a relentless aim, is also a good friend who offers help when it’s needed. In the second season, we see how she starts having special feeling for Hal, with who she maintains a serious relationship in the third season.

John Pope (Colin Cunningham)

He is the leader of a criminal gang in the first season, taking by hostage some of the members of the 2nd Mass, led by Tom. They escape and apprehend him.
Pope is smart, witty, charismatic, and he hunts skitters for fun. He got to admit that the invasion is the best thing that has happened to him. During the first season, tired of the poor quality of the food he becomes the chef, showing that also he has culinary skills. He invented the ammunition for weapons capable of destroying Mechs. He participated in the attack of the 2nd Mass to alien base in Boston. During the third season has become even more important in Charlestone, he also owns the pub. Keep leading the Bersekers, a group of soldiers in the 2nd Mass and he forms stronger links with Tom and even with Weaver.

Colonel Weaver (Will Patton)

Daniel Weaver is a veteran soldier, with a sensible attitude. In the first season he shows little patience with civilians.
He lost his family in the initial attack, so he tries to leave his past forgotten and focus on helping the resistance. In the second season, he discovers that her daughter Jeanne is alive, thanks to her, we will see a side of him more affable, sensitive and understanding. He is one of the cornerstones of the resistance, and right hand of Tom Mason.

Karen Nadler (Jessy Schram)

Before the invasion, she was a high school student. The day of the invasion, she left school to climb a tower for observe the ship. If she hadn’t, she would have died with the rest of the students in her class.
She joins Tom and maintains a relationship with Hal. When  they are trying to rescue Ben, she is taken prisoner by the skitters. From that moment, she becomes the greatest enemy of the resistance. In the second season she is shown as the right hand of his master, a Espheni. At the end of the second season, she implants a prove in the cerebral cortex of Hal (kissing him), which makes him an evil-Hal during the third season. In the third season, she is the leader of the Espheni, being the new Overlord and plotting against those who were his family and friends.

Brigadier General Jim Porter (Dale Dye)

He is the commander of the regiments of Massachusetts. In the first season, he was the one who decided that Tom will be the right hand of Weaver to allow civilian’s voice be heard in military decisions.
In the second season, he is revealed as Brigadier General of the First Army Continental in Charlestone. In the third season he is a critical part of the new government and he helps to make key decisions.

Tector Murphy (Ryan Robbins)

Before the invasion he served in the Marine Corps of the United States as sergeant at arms in the wars in Iraq and Afghanistan. But his team was ambushed in Afghanistan, and three soldiers were killed, making him to feel guilty.
Therefore refuses to participate militarily in the 2nd Mass, until Weaver changes his mind, thus becoming the best sniper and active part in the fight against the aliens.

Lyle (Brad Kelly)

One member of the Berserkers, group led by Pope. In the third season he also works as bartender at the bar of Pope.

Jeanne Weaver (Laci Mailey)
She is the eldest daughter of Captain Weaver whom he believed dead. She reappears in the second season, when Hal and Ben discover a group of young people calling themselves “Lost Boys” and take them to the 2nd Mass, where Jeanne is reunited with her father. Weaver asks her to go with them to Charleston, however, she decides to stay with her boyfriend Diego. Later she meets with her father in Charleston and during the third season she shows that she and her father have created a very strong bond. She also becomes a soldier and collaborates in some missions.

Denny (Megan Danso)

She’s a girl who it has removed the harness, and she fights alongside the rebels skitters. Shown as someone very close to Ben, she even calls him “Benji” in some or other scene.

Marina Peralta (Gloria Reuben)

At the beginning of the 3rd season she is the right hand of Tom regarding issues of the presidency, but when he leaves the town resigning as President, she accepts the post, becoming the new President of the New United States of America.

Roger Kadar (Robert Sean Leonard)

Dr. Roger Kadar is a scientist who lives in the basement of Charleston, where he has his laboratory. He helped to create the electric grid of Charleston, and he is willing to help but he has a phobia of go to the surface. Finally, because of they need his help, he comes to the surface and displayed as a new fundamental resistor pieces.

Alexis Denise Glass-Mason  (Erika Forest)
She is the newborn daughter of Anne and Tom. At first she looks like a normal human baby, but her strange behavior and DNA tests show that she is more alien than human. Her mother, Anne, takes her away from Charleston, they were kidnapped by Karen, whom at the end of third season takes them back to their own, but Alexis is now a girl of about 5 or 6 years, only weeks later. This girl is responsible for removing the bugs that Lourdes has inside, making it clear that a new alien-human race has come to Earth.

Cochise (Doug Jones)

Cochise is a Volm that lands on Earth willing to help humans fighting the Espheni. He has more humanity than most humans. He soon becomes a friend of Tom and although many of the 2nd Mass do not trust him, he slowly gains their trust. He was born destined to fight in the war, lost his brother and his father is a Commander Volm.