Background Information

Simon Tam was born in 2490 and raised on Osiris, a Core world planet.   He was highly intelligent and attended medical school where he was in the top 3% of his class. Simon Tam became a gifted trauma surgeon, and had a very promising career.   That all changed when he became worried about the treatment of his younger sister River, at the Alliance run Academy she was attending. He was able to decipher letters she wrote him which were unusually full of spelling errors and made up events, and was determined to save her. 
 
Simon was able to rescue River, with the help of an underground group who informed him of experiments the academy were performing on her. He enters the Academy dressed as an Official of the Alliance, and questions Dr. Mathias (the man in charge of her experiments) while he is performing an experiment on River. He incapacitates the doctor using a stun grenade. He and River then escape through the elevator shaft on a waiting lift attached to a ship above.  Simon is now a Fugitive.  

Life Aboard Serenity

Simon boards Serenity at the Eavesdown Docks, on Persephone with a large case. The case is later revealed to contain his sister, River.   The Captain is suspicious of Simon, and believes he is an undercover Alliance agent. That suspicion is soon put to rest when the real agent, Lawrence Dobson shoots Kaylee, while trying to apprehend Simon. It is then revealed to the crew that Simon is a fugitive, and Simon refuses to assist Kaylee unless Mal promises to not hand him over to the Feds.   
 
Mal offered Simon the role of Medic aboard Serenity, although he does not yet accept him as one of him crew.  Jayne causes tension with the Tams, and even goes as far as trying to sell them out to the Alliance.  Slowly Simon becomes closer with the crew, especially Kaylee.  Simon and Kaylee have a relationship which develops into something more than friends.   Simon is compassionate, extremely smart, very gullible and seems to lack some interpersonal skills, as he often says the wrong thing.   
 
Simon Tam was portrayed by Sean Maher in the TV series “Firefly” and in the Motion picture “Serenity”.  
Young Simon was portrayed by Zac Efron in the “Firefly” episode “Safe”.