According to Cherry, casting the role of Karl was difficult because he "wanted a guy that was nice looking and seemed like he would have been married to Teri, but was also someone you wouldn't like." The character was portrayed by another actor in a series of non-speaking flashbacks in the pilot episode, but the role was recast once the direction of the character changed. After making some guest appearances during the first season, Burgi joined the regular cast in the second season. However, he returned to his guest starring status from the third season until his character's death halfway through the sixth season. Burgi returned for the series finale, appearing as his character's ghost among other deceased characters.
History
Season 1
Karl and Susan Mayer divorced a year prior to the events of the series as a result of Karl's affair with his secretary, Brandi. In the season one episode "Move On", Karl ends his relationship with Brandi and asks Susan for a second chance, but she declines because of her commitment to Mike. Susan also discovers that he flirted with Edie while they were married, and soon Karl starts dating Edie.
Season 2
Susan discovers that Karl is now living with Edie. However, he is jealous of Mike Delfino and tries twice to get back with Susan. He even goes so far as to lie to Susan and say that he was breaking it off with Edie, which led to him and Susan having sex. It is made obvious that Karl is still in love with Susan, as shown by several pictures of her that he secretly keeps around the house for him to look at from time to time. Later Bree Van de Kamp hires Karl to stop her son, Andrew Van de Kamp from blackmailing her. Karl tells Andrew that even though Bree did witness George Williams die, she will not even face a courtroom. Andrew says that he will just make up stories or give her a "public humiliation" and Bree is horrified, Karl asks Bree for more tea and as Bree leaves for the kitchen, Karl grabs hold of Andrew and puts him against the wall and he says that he was a good friend to his father Rex Van de Kamp and said he knew if Rex was alive then he would force Andrew to behave. Andrew backchats once more but Karl grabs him by the cheek and says that if he doesn't stop blackmailing Bree and not giving her the respect she deserves then he will take care of Andrew himself. Bree overhears from the kitchen and lets out a sigh of relief. Later in the season, Karl offers to marry Susan when she needs a life-saving surgery so that she can use his health insurance to pay for it, but they plan to divorce soon after Susan's surgery. Karl becomes jealous of Susan and Dr. Ron McCready's relationship and he knows that Susan had not yet mentioned her and Mike's past, so Karl breaks open a pipe under the sink and Ron gets Mike and he learns that Susan had lied to him and Karl watched happily as Ron dumped her. Later in the series, Karl asks Edie to marry him; however, when Edie learns of their sham marriage, she demands that Karl propose to her and throw her a lavish wedding. Karl and Susan sleep together one night and, as revenge, Edie burns Susan's house down, prompting Karl to buy her a new one as another attempt to get her back, only to be stopped by Mike. Karl eventually leaves Edie.
Season 3
Karl appears only in the episode "Children and Art" to play the bad cop for Julie and Austin McCann. This backfires when he gets mad at Susan for dating Ian Hainsworth, a married English man whose wife is in a coma.
Season 4
Karl returns when Susan meets him at a Lamaze class as his pregnant new wife, Marissa, was there; Mike was not there as he was receiving his 30 days chip. Karl constantly teases Susan about how things are going for him including Marissa being an author and a law student and him becoming partner of his firm and he constantly puts Mike down for referring to him as "the plumber". Susan however brings Mike along to the next class and makes herself and him dress up in order to impress Karl, where they both lie and say they have a party to go to after and that Mike now owns his company however Susan becomes disappointed when Mike mentions he was in rehab. When Susan confronts Karl, he tells her that Mike is a good guy and he'd be better for her then he ever would. In the five year leap on season five it's presumed Karl and Marissa had their child.
Season 5
Karl reappears in the second episode of the fifth season, where he was asked by Julie to pick up and help her with her insurance. He tells Susan he has been talking to her new love, painter Jackson Braddock, and teases her that she has now had a plumber and a painter and if he was a roofer they might still be together and Susan asks him to leave. Karl reappears yet again in the eighteenth episode of the fifth season, "A Spark. To Pierce the Dark.". Karl has enrolled his son Evan in Susan's art class, Susan gave the class an art assignment to draw what makes them happy and Evan drew his Mom being pierced with a sword. Susan felt concerned by this and called Karl to talk to him about his picture and Karl had confessed to Susan that Marissa had left them 6 weeks prior because she could not handle being a mother, and now Karl is caring for Evan by himself. Karl comments that he finally understands why it bothers Susan to see him and that he was truly sorry. Susan said that while she always wanted Karl to feel what he had done to her, it was not a great feeling and she was sorry that it happened to him. Bree later hires Karl as her divorce lawyer. When Bree's husband, Orson Hodge, blackmails her into staying in the marriage, Karl and Bree begin an affair.
Season 6
Karl and Bree continue their affair during the first part of the sixth season. Karl decides to propose to Bree during the annual Christmas party, even hiring an engine plane with a banner behind it with the message "Will you marry me, Bree? Love, Karl" to fly over Wisteria Lane. Karl shows up in the party and tells Orson about the proposal and the two get into a fight in Santa's Workshop. Bree notices the activity going on inside Santa's Workshop, and goes in to stop Orson and Karl from fighting. When the plane slides into the party, it smashes into Santa's Workshop and after the crash a bloody hand is hanging out from one of the Workshop's windows. It is revealed in the next episode that Karl died from his injuries from the crash. Part of the episode is devoted to Susan wondering what would have happened to her life if she had not divorced Karl, while another part centers on Bree contemplating a hypothetical marriage to Karl. In his will, Karl leaves Susan his partial ownership of a local strip club.
Season 8
Richard Burgi makes one last, uncredited appearance as Karl in the series finale, "Finishing the Hat", as one of the ghosts that watch Susan and her family leave Wisteria Lane.
