|Family & Friends|
|Parents|| Ida Welker (mother)|
Victor Welker (possible father)
Radu Gogorsky (possible father)
|Siblings|| Lois Wilkerson (half-sister)|
Roberta Welker(possible half-sister)
|Portrayed by||Laurie Metcalf|
Susan Welker, portrayed by Laurie Metcalf, is Lois' younger sister who appeared in Season 5's "Lois' Sister". Before, she was mentioned a lot. It was revealed that Susan was the clear family favorite and was more talented than Lois. She was often called on a lot of times by Ida whenever she needed help. In the first part of Baby, Susan had a brief misunderstanding with her mother that led her to move in with Lois for a while. She later called Ida to clear up the misunderstanding and she moves in with her. Susan gave Lois hell for being hopeless and untalented during her visit and it made her reflect on how unmotivated Reese was.
Susan finally makes her first appearance in season 5 and despite being cordial to Malcolm, Reese, Dewey and Jamie and giving them presents, she was very bitter with Lois for years. This in turn lead to a huge fight between them when it's revealed that she still blames her for stealing Hal away from her and it lead to her unmarried status. When Lois learns that Susan is dying of kidney failure, she offers one to her. She intitally refuses to take one of Lois' kidneys and states that she'd rather die. Susan also believes this is her pathetic attempt to get ahead of her. Lois pleads with her to accept one of her kidneys because despite their past problems, she still loves her. Susan ungratefully and begrudingly takes one of the kidneys.
Susan was mentioned in Season 6's Living Will, when Lois snapped Hal of his fake paralysis and told him he made the right decision to marry her over her sister. She was both families choice of wife for him because she was high class and talented.
Susan was mentioned in the last episode of the series Graduation, discussing with Lois on the phone cause she was not invited to the Malcolm's graduation; Lois says the her mother "bullied her" into giving her the last ticket they had for graduation (this possibly in order to see how Reese screwed up the graduation's ceremony with his prank). Although in actuality, Susan had gave Ida her ticket so she doesn't have to attend Malcolm and Reese's graduation since she still blames Lois for foiling her chances at death.
- It was revealed in season 4's Garage Sale, Susan was more talented than her and was always encouraged to do better. She gave Lois a hard time about it and it was reflected on Reese(though it was later revealed that he doesn't care about being unmotiviated and is almost just as greedy as Ida).
- In Season 5's Lois' Sister, it was revealed that Hal Wilkerson used to date Susan and that both families wanted him to marry her. However, he chose to marry Lois against their wishes and it lead to conflict between Lois and Susan for years.
- There are many references in "Lois' Sister" that are a homage to Metcalf's performance in wikipedia:Scream 2, Susan is crazy as her scream 2 character Debbie Loomis was (though much more insane). Lois mentions that her bully, Sidney Bower, was beaten up by Susan to protect Lois. Sidney is the name of scream's protagonist Sidney Prescott and Debbie Loomis did try to kill her.
- In Season 5's Victor's Secret Family, it's possible that Susan could be Victor's daughter with Ida and that she and Lois are half-sisters. It's also possible that she's eligible for his pension and may be related to Roberta.