Dr. Simon Tam is ship physician on Serenity. He got that job by going up against the Alliance, and that tickled Serenity Captain Mal Reynolds enough to hold on to Tam as medic, although from time to time Mal gets miffed and is ready to throw Simon and his kid sister off the ship, though he never really does.
Simon comes from an affluent and important Alliance family and was once an Alliance supporter, but is now, like Mal, a fugitive who escaped being bound by law more than once.
Simon was in the top 3% of his Medical School class and was a very well-to-do surgeon at a big city Alliance hospital before he gave up everything to spring his sister by force from an Alliance controlled center that was fooling with her brain and trying to condition her as a seer and soldier.
Simon goes through life forgetting (figuratively) to remove the coat hanger from his shirt. In short he's a stuffed shirt and retentive and can sometimes be a stuck-up snob. But he has his moments, especially with his kid sister River, whom he adores and always has, or with Kaylee, the ship mechanic, or Inara, the ship's companion. Simon sometimes loosens up. He sees Kaylee and knows she likes him, and he knows she's cute and likes her back, but he just can't get down in the mud and play like his little sister River can. He gets caught drunk in a bar sleeping with Kaylee on top of him and he's all prim and proper and saying he never touched her.
He's the only one who can miff Kaylee more than Serenity Captain Mal Reynolds.
Simon can even plan a great crime if he wants to, if it serves a purpose, like helping River.
Simon also can't ignore someone in physical need. If he's abducted he'll treat his abductors if required. If he's trying to fix River and someone nearby is dying he'll tend to them.
His detachment comes naturally, being a professional who deals with death and dying.
Young Simon was played by High School Musical star Zac Efron
in his first TV role at the age of 13 in the TV episode Firefly: Safe (#1.7)
. Dr. Simon Tam was played by Sean Maher
throughout the series and feature film Serenity