Walter Wilkerson, played by Christopher Lloyd, is Hal's eccentric father and head of the Wilkerson Family. His daughters are named Claire and Amelia and has grandchildren from all of them. Since Hal came from a wealthy background, he and his wife, Sharon, wanted him to marry a high class woman. Walter and Sharon originally supported him marrying Susan. Despite this though he supported Hals decision to marry Lois and only mistreated her in secrecy. Whereas Walter's wife, Sharon, and daughters Amelia and Claire made their point across that they'd rather have Hal marrying Susan and vehemently voiced their disgust over him marry a low-class control freak like Lois.
It was revealed in season 4's Family Reunion, that Walter never listened to Hal and tickles him when he came to confront him about the way he and the rest of the family are mistreating Lois. This however came back to haunt him, when Hal showed up in several layers of coats and tickled him back. This forces Walter to confess why he and the rest of the family continued to mistreat Lois the way they do. He and Sharon had approved of her younger sister, Susan, because she was higher class and talented. His reason for never listening to Hal was because growing up Hal had lot of Problems the other kids didn't have and he didn't know how to help.
They were displeased with Hal when he willingly married Lois over her. They thought she didn't deserve to marry him because Lois was untalented, had a lower background (though this is senseless because Susan comes from the same background) and was classless with her loudmouthed, pushy personality. Out of the boys, Walter likes Malcolm the most because of a similar love for history and amateurishly tried to reenact a Civil War scene.
In the episode Victor's Other Family, Hal apologizes to Dewey for letting him down and says that he's been let down before too. He then starts to tell him the story of a time when he was his age and his father promised to take him to an air show. The entire story was not heard, but it can be implied that Walter broke that promise to Hal.
In the episode Hal Grieves, Walter dies, being revealed by Reese that he had lost all his money before dying, and Hal has a hard time expressing grief because he never paid attention to him. Fearing the same fate that befell on him, Hal tried to overcompensate with gifts and allowing the boys to miss school so they will love him forever when he dies. While Reese and Dewey took advantage of it, Malcolm realizes it's wrong and tried to stop him. Hal was able to finally grieve for Walter when Lois finally stepped in.
- Due to Walter dying in the series, both the Wilkerson boys' maternal and paternal grandfathers are dead by the end of the end of the series, with their maternal grandfather, Victor Welker having been mentioned to have died in the episode Christmas. That is if Victor was their grandfather and not Radu Gogorsky.