River Tam (Summer Glau
in a truly inspired realization) is the 17 year old genius sister of Dr. Simon Tam (Sean Maher
), both born into a very affluent and prestigious Alliance family in Central City.
As a young child (played by Skylar Roberge
in the TV series episode Firefly: Safe (#1.7)
and as a young teen by Hunter Ansley Wryn
in the feature film Serenity
dream sequences) she was playful, precocious, full of imagination, extremely bright, correcting the homework of her older brother "Young Simon" (played by Zac Efron
in his first TV role in the 'Safe' TV episode), while criticizing the conclusions of published text book experts. The two of them would engage in games and adventures which included raiding the neighbors yard for berries or pretending they were Alliance fighters who had to resort to cannibalism and eat their own men because they were out of food.
She was well versed in spelling and grammar from the age of 3, understood Quantum mechanics, physics, biological functions and took dancing lessons (Summer Glau was a trained dancer and did a jig with the locals on stage in the episode Safe). When she was 14 she and her well to do family learned of a special Academy run by the Alliance for gifted students and River insisted upon going to that Academy. Once at the Academy the scientists there began to experiment with her brain (cutting into it), developed her in the areas of being a seerer or mind reader, plus she was also trained for combat and programmed to fight on command. This training program hurt and bothered her immensely, but her communications with the outside world was limited as to what she could write to her brother and family. She sent cryptic messages in the form of code trying to tell them to come get her. Simon, who had always shared a close, symbiotic relationship with this precious little 'brat' of a sister (who would pester him until his put down his studies and gave her willing quality time) started to get worried about the nature of her communications. Risking his job and his position as a respect surgeon in an Alliance hospital Simon started to talk with people in the underground to see about getting her out of that Academy.
Simon brings River on to the transport ship Serenity (in the TV series pilot episode Firefly: Serenity (#1.11)
in cryo-stasis where she is released by the Captain, Mal Reynolds (Nathan Fillion
), who becomes immediately protective of River. Mal is always concerned about her state of wellness and began to see her as having full, adult crew member potential. Kaylee (Jewel Staite
) the ships mechanic, takes to playing with River like a best friend or sister, even though Rivers action sometime give her some concern. Jayne (Adam Baldwin
) the tall, muscle man warrior, thinks of her as moon-brained and being in the way. Wash (Alan Tudyk
) the pilot, as the voice of reason on the ship, always calms the waves when River is attacked. His wife Zoe (Gina Torres
) a realist and warrior, just sees the situation as it is and points out the obvious that at times they would be better off without River and Simon. Professional Companion Inara (Morena Baccarin
) and Preacher Shepherd Book (Ron Glass
) tend to back Wash, directly or indirectly, as the voice of reason. Rivers real brother Simon, however, sees her as more like his own 2 year old toddler whose hand he has to hold for dear life.
As River starts to explore her new world on the ship (in the TV series 'Firefly') everyone starts to take slow notice of her Alliance training in reading or seeing people thoughts as well as displays of her combat training. On the TV series River was a 'work in progress' and often just part of the background (at times she doesn't even speak). We know her to be soft-spoken, emotional, empathic, wise and even brave. She also feels very guilty about taking her brother (whom she is very proud of) from his career as a surgeon due to her desire to go to the Alliance academy and his rescue efforts.
The show runner (Joss Whedon
) was trying to develop her but the show was cancelled before he could, so in the theatrical movie, Serenity
, which came out 3 years later, River became fully developed and was the central thread of the whole movie. River had long thought of Mal as a surrogate father to both her and Simon (as did most of the crew), Jayne was her mean little brother or neighbor's kid, whom she like to torment in retaliation for his torment of her and Simon, Kaylee was her bestest of friend (having a crush on brother Simon), Inara (estranged as she was from Mal) was a step mother (being the only one who could boss Mal around and get away with it, as well as being a voice of reason), Wash and Zoe as aunt and uncle.
The crew was Rivers true family and the ship, Serenity, her home. River and Mal would dance around each other, sizing each other out and standing their respective ground. This began with "Safe" and later "Objects in Space" (Firefly TV episodes) and picked up again at the start of the feature Serenity when Mal takes River on their crime wave against the wishes of daddy Simon who doesn't think his toddler, River, is ready to go play with the other kids in their cowboy and Indian games. In the feature, Serenity, River comes to full blossom and Jayne even comes to respect her wisdom and empathic abilities, not to mention that everyone comes to respect her considerable combat skills. River is the special one. River is the key to all there is in their verse. River, in her own way, leads Mal to the belated victory for the of the battle of Serenity Valley. The battle that Mal and Zoe lost. The battle that cost Mal his faith and belief. This horrific reality that River leads everyone into puts Mal and the crew on a collision course against the Alliance and its evil operative (played by Chiwetel Ejiofor
in an outstanding performance) who is out to stop Mal and River at all costs.