Sam Allen is Rex's illegitimate son.
Conceived shortly before his father, Rex, met and became engaged to Bree Mason, Sam grew up in a poor household and spent most of his early years living in a small house (with no central heating) with his mother, Lillian. Rex discovered he had a son and, seeing the way he was living, offered Lillian a choice; Sam could live with him and Bree and be given the perfect childhood, or he could continue living with her. Lillian decided to keep Sam. Rex visited Sam and Lillian occasionally, however, Sam always viewed himself as second-best to Rex's other children, Andrew and Danielle. He regularly stood across the street from his father's house on Wisteria Lane and watched the goings on of the family through the windows, envying the lives of his half-brother and sister. Sam came to despise his mother because of her choice to keep him.
Sam visits Bree and asks for a job at her company. He quickly wins Bree over with his business know-how, but he receives heavy criticism from Andrew, who believes he is hiding something. Later when Bree goes to drop off a basket of muffins after Sam and Andrew get into a violent fight, she discovers that Sam is Rex's son. Bree is shocked by the revelation but later decides to speak with him. He reveals that Rex and his mother had a one night stand before he met Bree and they produced him. Rex visited him a few times but after a while Sam's mother asked him to stop, citing it hurt Sam too much. Sam tells Bree he always wondered why Rex chose his new family over him and this makes Bree feel guilty. Bree decides to incorporate Sam into the family and organizes a family dinner (including Danielle) so everyone can get to know each other. Sam becomes a rival to Andrew in the company, as well as for Bree's affection. He tries to discredit Andrew and prove him unreliable. Sam plots to make Bree fire Andrew, which she later does, but after she reveals to him that since she has a love-and-hate relationship with her son, and it's most likely that Andrew would return. After, an important client dinner is sabotaged, Sam points a finger at Andrew. When Bree tells Orson what occurred, he says that it couldn't be Andrew because it's seems something well planned, and Bree begins to suspect Sam's true intentions. Bree's suspicions also arise when Sam acted weird around a woman who was working at the grocery store they were shopping at. Wanting to know the truth, Bree visits the lady and finds out it's Sam mother. Bree is shocked because Sam had previously told her his mother had recently died. When Bree confronts Sam, Sam reveals that a few months before he started working for Bree he discovered a letter from Rex offering assistance to raise Sam. When Sam asked his mother about the letter, she says that she declined his offer and decided to raise Sam on her own. Sam tells Bree that he was extremely angry at his mother at robbing him of a chance with his affluent father. When Bree tries to reason with Sam, Sam violently yells at Bree and throws a vase across the room. Bree becomes scared of Sam and decides to tell him to leave. Sam retaliates by telling Bree he will not be going anywhere. Bree attempts to use two detective friends to threaten and scare Sam but her plans fail.
When Bree finally pushes him too far, Sam tells her that if she doesn't hand over her company to him then he'll tell the cops Andrew was the one who ran over Carlos Solis's mother. Sam tells her that a drunken Danielle had told him about the incident at the dinner party in an attempt to bond with him. At the end of season six, Bree signs over her company to Sam, but gives him the ominous warning that if he continues down the path he's chosen in life, he'll end up with no friends or family that care about him. This seems to strike a chord with him, but he leaves nonetheless.