"Here's how it is: The Earth got used up, so we moved out and terraformed a whole new galaxy of Earths. Some rich and flush with the new technologies, some not so much. The Central Planets, thems formed the Alliance, waged war to bring everyone under their rule; a few idiots tried to fight it, among them myself. I'm Malcolm Reynolds, captain of Serenity. She's a transport ship; Firefly class. Got a good crew: fighters, pilot, mechanic. We even picked up a preacher for some reason, and a bona fide companion. There's a doctor, too, took his genius sister outta some Alliance camp, so they're keepin' a low profile. You understand. You got a job, we can do it, don't much care what it is. "
Capt. Malcolm "Mal" Reynolds (Nathan Fillion)
During the war of independence, Mal enlisted on the independent side, fighting against the Alliance as a sergeant in the 57th Overlanders. He was part of the "Browncoat" force on Hera holding Serenity Valley for over a month, before the Alliance finally overwhelmed them. A born leader, Mal kept his troops' morale up in the most hopeless of situations. Once a devout believer in God, the end of the war saw him losing his faith.
After the war, Mal purchased a battered old Firefly-class ship, which he named Serenity, and took jobs as they came. He remains a born leader, and is fanatically dedicated to his crew. He is not, however, a born strategist, and his plans often tend to go a bit wonky. Still, he inspires fierce loyalty in his people.
Zoë Warren (Gina Torres)
Zoë enlisted with the independents during the war, serving as Mal's right hand in the 57th Overlanders. After the war, she became his first mate on the Serenity. Loyal to Mal at all costs, Zoë is also a crack shot and deadly in a fight. When Mal's plans inevitably go bad, Zoë is one of the reasons why it doesn't put them completely in the crapper.
She is married to Wash, the ship's pilot.
Hoban "Wash" Washburn (Alan Tudyk)
Hired by Mal to pilot the Serenity, Wash came with dozens of recommendations, all deserved. One of the best pilots in the 'verse, Wash also brings a laconic sense of humor to the Serenity. Accompanying him in the cockpit are some toy dinosaurs, which he sometimes uses to act out various dramas. He also has terrible taste in shirts.
Kaywinnit Lee "Kaylee" Frye (Jewel Staite)
Kaylee wasn't aboard Serenity for an hour before she diagnosed and fixed a problem that was keeping the ship grounded — all without ever having set foot in a Firefly-class boat before. "Natural talent" is how she says her father describes it, and Mal hired her on the spot.
Kaylee is a good soul, thinks the best of everyone, and always has a sunny disposition — even when she's scrambling to fix something that's broken on Serenity while they're at full burn running from the Alliance.
Kaylee is also sweet on Dr. Simon Tam, though he only occasionally notices.
Jayne Cobb (Adam Baldwin)
A mercenary, Jayne was working for a competitor of Serenity's when he got the drop on Mal and Zoë. He switched sides when Mal made him a better offer, and he has remained on Serenity since then.
Jayne's guiding star is what is best for Jayne Cobb — self-interest is his only interest. He excels at violence, which is why Mal keeps him around, despite the legitimate concern that he might betray any one (or all) of them if the price is right.
Inara Serra (Morena Baccarin)
A licensed Companion, trained and skilled in many forms of love-making, Inara brokered a deal with Mal to rent one of Serenity's shuttles as her residence and place of business.
Inara left the Companion House on Sinhon in order to be on her own, on a ship that travels mostly between the outer planets — an unusual choice for a Companion.
Inara's presence lends an air of legitimacy to the Serenity's crew and activities, and she has fallen in love with life on the ship. She also gets along well with most of the crew, though she struggles to make sense of her complicated love-hate relationship with Mal.
Dr. Simon Tam (Sean Maher)
Simon was one of the finest doctors on Osiris. His parents sent his gifted younger sister, River, to the Academy, an exclusive school where she could learn with other brilliant children … or so they said.
He grew concerned when he didn't hear from River for months — and then he suddenly received letters from her that seemed to be nonsense, but were in fact written in a code that said that she was being hurt. Against the wishes of his parents, and exhausting his entire personal fortune and damaging his medical reputation, Simon broke River out of the Academy and traveled to Persephone, where he booked passage on the Serenity.
Simon and River are both fugitives from the Alliance. Mal has agreed to let them stay aboard the Serenity, chiefly because Simon's medical skills are sorely needed by the crew.
River Tam (Summer Glau)
River possesses powers that are a threat not only to the forces pursuing her but also to the Serenity crew, who have given her sanctuary.
Before being rescued by her brother, Dr. Simon Tam, she spent years enduring experiments in an Alliance lab, and the experience has left her forever altered. She is certainly a genius of sorts, but one who is tortured by her own intellect.
Most notably, she is borderline psychic and can read most minds. Because of this, she has an incredible comprehension of knowledge and data, but it can lead to unpredictable and chaotic behavior.
In addition to her heightened mental abilities, she is also preternaturally dexterous and highly skilled in martial arts and weapons combat. However, these gifts appear infrequently; most of the time she swings between catatonia and manic, gibbering fits.
Shepherd Book (Ron Glass)
Book came aboard the Serenity at Persephone, telling Kaylee he had come from Southdown Abbey and wanted to "walk the world a while." Paying for his passage with real fruit — a rare thing for the crew — Book's spiritual nature is a marked contrast to the grittier nature of the crew.
There are exceptions, though; there is more to Book than meets the eye, as he possesses intimate knowledge of things outside the purview of most "people of God".