Katherine "Kate" Daphne Halligan Tanner is the mother figure, played by Anne Schedeen. In addition to her mother, who plays a role in the series, she has at least one sister (although she once tells ALF that she was an only child). She majored in art history and sometimes works in real estate. Like her husband, Willie, she was a flower child during the 1960s.
Kate doesn't appreciate how her mother still treats her like a child. In episode Mother and Child Reunion, ALF got sick of living in the garage so he can be hidden from Kate's mother, and his first option was putting up a sign that said "Alien On Strike" with the back side saying "Unfair Living Conditions". His second option is to pull Kate and her mother together, and Kate explains at the end that she feels that her mother doesn't think Kate can do anything right. ALF even put a private conversation of Kate saying how much she wants her mother to leave in the next episode A Little Bit of Soap into Dorothy's favorite TV show One World To Hope For. This was so ALF can spill the beans of Kate's secret feelings to her mother. But then ALF decided to put Dorothy and Kate in the scripts that Kate deserves as much power of a household as her mother used to, and both women make up.
She is more mature than most other female characters on the show. Her friends such as Sylvia, her mother, and Raquel Ochmonek, compared to Kate, are immature and less serious than Kate. Kate has an extremely serious character, even being strict towards ALF since the first episode and being the only one in the Tanners family who did not want ALF around in their house in the pilot episode.
ALF has accidentally walked in on Kate while she was showering at least twice. One time was in the Season 1 intro, where he was using a video camera to record her coming out of a shower, demanding ALF to leave, and the 2nd time was Wild Thing where she threatened ALF, "You do that again, you're a seat cover!"
Kate is the most pessimistic, sarcastic, and strict member of the Tanners' family household towards ALF and all other topics. Most episodes involves Kate in a bad mood or bad situation, and several episodes' plots involves ALF becoming punished or scolded almost always by Kate.