"...no matter how each of us survive, maybe we owe it to those who didn't, to become the best of mankind."
A former history professor, Tom lost his wife early on in the invasion, and he was left alone to keep his three sons safe. He joined the Massachusetts Militia with his sons, but his second oldest son Ben was captured and put into a harness when the invasion began, but was eventually rescued. Tom serves as Weaver's second in command of the 2nd Massachusetts.
Properly Paranoid: After returning to the 2nd Mass after the aliens let him go, Tom insists that every keep an eye on him and stop him if he starts acting weird, due to his fears of brainwashing. The parasite in his left eye that Anne extracts that later escapes and goes to Red Eye shows his fears are not unfounded.
Tom's second oldest son, Ben was captured by the aliens and put into a harness while fighting for the 2nd Massachusetts. He was eventually rescued and freed from the harness, but is now suffering from some side-effects.
"You don't have to agree, you just have to follow orders."
A veteran of Operation Desert Storm, Weaver is placed in charge of the 2nd Massachusetts. He has little regard for the needs of the civilians with the unit, viewing them as a hindrance to fighting the aliens. He eventually grows out of this viewpoint and comes to rely heavily on Tom's advice.
Heroic BSOD: Weaver goes through one of these after being exposed to one too many reminders of the family he's lost. He snaps out of it when he finds his wife's glasses and realizes she may still be alive.
The Lost Lenore: The loss of his wife (and daughter) made Weaver quite a bitter man.
Made of Iron: Out of the entire main cast, Weaver is the one more likely to be poisoned, shot at, stabbed or be thrown through windows, yet he survives, every time. Lampshaded very frequently, such as Mason's off-hand comment that "Weaver is made of cast iron". However, these wounds are starting to take a toll on him, as seen by his recently discovered heart problems.
Tragic Keepsake: If you look carefully, you'll notice his hand has a small band wrapped around it. That band belonged to his now deceased wife.
Karen Nadler (Jessy Schram)
A scout with the 2nd Massachusetts, Karen is dating Hal. She is captured by the Skitters during the rescue of Ben and put into a harness. She later returns as the mouthpiece of an Overlord who talks with Tom.
Alas, Poor Villain: Played with. In her final moments, she apologized for her actions and confesses her love to Hal, but we have no clue if she was being sincere or not, and no one except Hal seems to believe her words (specially Margaret, who actually shoots her mid-sentence).
Villain's Dying Grace: By accident. She releases Anne and Lexie (who were previously thought to be dead) as a token of peace towards humanity, but unexpectedly Tom shoots her dead mid-way through the conversation, and as a result her final act is releasing Anne and Lexie.
Would Hurt a Child: Admits to Tom she would hurt Tom's newborn daughter to get the necessary information.
Margaret (Sarah Carter)
A unwilling member of Pope's band of marauders, Margaret helped the captured members of the 2nd Mass escape and kill them. She then joined Tom's squad, and quickly grew close to Hal.
Action Girl: Seriously shown in the season three premiere, where she takes on three harnessed kids by herself and when she runs out of ammo charges at the next one with her knife.
Defrosting Ice Queen: Nonromantic with the entire group over time (and somewhat romantically with Hal), starting with how she treated Jimmy during an attack.
Despair Event Horizon: She seems to have crossed it when she had cancer. After she was cured, she could only see the world as fake. It's unclear if she's come back yet, but her rape probably didn't help.
Vitriolic Best Buds: Starting to develop this with Pope, though he will still side with the rest of the 2nd Mass in an argument against Pope. Plus he hasn't forgiven him for the fact that one of Pope's marauders killed his friend Click, but also notes that Pope saved his life back in Boston, so he is not sure what to make of Pope.
John Pope (Colin Cunningham)
"Life hands ya lemons, ya blow its friggin' head off."
The leader of a gang of racists and rapists, John captured Tom and his squad in an effort to get the 2nd Massachusetts .50 caliber machine gun and food stores, but failed and was captured by them. He has since joined up with the 2nd Mass as the leader of a squad called the Berserkers who shared his bloodlust and hatred of the Skitters.
Never Found the Body: Dai was visiting headquarters when it was attacked, and brought word back to the 2nd Mass that Porter was leading a last ditch defense. All contact was lost with command after this, and Porter was assumed to be dead. He's revealed as alive in Season 2, and in Charleston.
My Greatest Failure: While serving in the Marines, Tector led his squad into an ambush that resulted in three of his men dying, and he blames himself he didn't properly look at the map of the area they were going to patrol and realize how dangerous the terrain was. When Boone gets killed, he blames himself again since he had been training Boone.
Nice Guy: Espically when compared to the rest of the Berserkers.
The Berserkers: "Crazy" Lee (Luciana Carro), Lyle (Brad Kelly), and Boone (Billy Wickman)
The Berserkers are a squad founded by Pope which consists of several members of the 2nd Mass who share his hatred of the aliens. They are usually given assignments which other squads consider too crazy to consider doing. Led by Tom Mason after his return to the 2nd Mass.
Hidden Depths / Smarter Than You Look: At one point, Anthony wonders "What are they waiting for?", Lyle, whose dialogue thus far has consisted of threats or nods of agreement, answers "Godot.". Even Anthony seems surprised by the answer.
Galactic Conqueror: His species has a knack for enslaving sentient species under any means necessary, and are shown to have done this at least once before, with the Skitters. Curiously, he's called "Overlord" In-Universe.
His first attempt at hand to hand combat is his last, as Tom effortlessly kills him.
No Name Given: We don't even know if his species use names, but if nonetheless we are never given a name for him, and so he's called by a wide variety of nicknamed (The Overlord, Fishhead, Espheni and so forth)
A Skitter aboard the ship Tom was temporarily held on. He followed the humans, was captured, and tells the humans through one of the rescued children that he's part of a Skitter resistance. Current location unknown, as he escaped in the attempt by Ricky and Ben to free him.
Badass: Effortlessly overpowers both Jimmy and Ben.
Big Damn Heroes: Saves the 2nd Mass strike team sent to destroy the Overlord's weapon, but dies fighting the Overlord.
Officer and a Gentleman: Absurdly polite and soft-spoken to the 2nd Mass, even though he is usually talking with numerous guns pointed at him. Further more, he always calls Mason "Professor Mason" or "Professor".
You Can't Go Home Again: Worse than the usual situation, as Cochise not only can't go back to his homeland (because of the war against The Overlords), but he has never seen his homeplanet in his entire life.
Commander Waschak-Cha'ab (Doug Jones)
The Volm in charge of the entire Volm expeditionary force on Earth, and Cochise's father.
Acting for Two / Talking to Himself: Doug Jones not only wears the make-up for both of them, but he also voice-acts them both (only with a digital enhancement for Waschak).
Hero of Another Story: He's been waging another, much larger and deadlier, war against the Overlords off-screen in the present, and in the past, he fought them across several planets.
Humans Are Insane/Humans Are Warriors: Seems to conflate the two because humans are the first race he's encountered who weren't happy to let his people do their fighting for them and go to a reservation