"Kill Gill, Volumes I & II" is the ninth Christmas episode of the animated sitcom The Simpsons, aired in the show's eighteenth season. This episode aired exactly 17 years after the very first episode ("Simpsons Roasting on an Open Fire"); it was also the fifth episode to air on this date. Elvis Stojko guest starred as himself.
The Simpson family is enjoying “Krusty’s Kristmas on Ice” (in an indoor ice rink), starring Elvis Stojko. The main act features a reindeer, a candy cane, and a snowman who are all fretting over a green monster named the Grumple, who advances upon the other Christmas characters, threatening to steal their Holiday Cheer (in a parody of How the Grinch Stole Christmas!). The characters mistakenly stumble backward over a wooden basketball court setup crew led by The Sarcastic Middle-Aged Clerk. All the Christmas characters are enraged that their show is being cut short and they begin brawling with the Utah Jazz as they try to warm up for a basketball game. Marge and the kids decide to get up and leave, and Homer is spotted down on the ice grappling with the Grumple and demanding back the Holiday Cheer. The Grumple repeatedly returns throughout the episode, wanting to kill Homer.
On Christmas Eve, the Simpsons go to Costington’s department store where a sad Lisa sits on Santa’s lap and explains the one true present she wants is the Malibu Stacy Pony Beach Party Set, which is sold out everywhere. Santa Claus, who is really Gil Gunderson (this episode reveals his last name), pities Lisa and goes back to the stockroom and finds an extra play set he had seen earlier. An overjoyed Lisa thanks Gil as a cashier rings up the sale. As Marge and the kids exit the store, an angry Mr. Costington comes out of his office and berates Gil for selling the Malibu Stacy play set that he had set aside for his daughter. When Gil refuses to take the present away from Lisa, Mr. Costington fires him. Marge and the kids witness the scene and feeling sorry for Gil, Marge invites him over for Christmas Eve dinner.
After dinner at home, Gil and the rest of the Simpson family gather around the piano and sing songs. Finishing, Gil gets up to leave; however, Marge insists he stay the night, citing how late and cold it is outside. Gil accepts Marge’s offer. On Christmas morning, Gil retrieves items from his bus locker, assuming he had a permanent spot in 742 Evergreen Terrace. Indeed, Gil’s weak demeanor and lack of job allows Marge to let him move in, and Homer is too distracted by the Grumple's presence outside the home (where it rhymes about putting Homer's blood in his stew) to pay much notice to Gil.
Gil begins to ruin their every holiday. However, Marge continually allows him to stay out of guilt, due to a childhood memory when Patty and Selma stuffed her in her own dollhouse for not hiding their cigarettes. Homer’s patience wears thin after Marge’s inability to say "no" causes Gil to walk in on Homer and Marge’s “snuggling” on Valentine’s Day, and bring his friends to sing and drink on St. Patrick's Day. After eleven months, Marge finally agrees to say no to Gil and kick him out, only to learn from Bart and Lisa that Gil got a job in Scottsdale, Arizona, packed up his things and left that morning.
Gil ends up becoming a very successful realtor in Scottsdale. Despite this, Marge wished to go there and finally get the pleasure of saying “no” to him. After Marge’s display of anger towards him and Gil’s cowering display of weakness, the other salespeople are disgusted by Gil, and Gil’s boss charges out of his office and fires Gil on the spot. Marge is horrified when she realizes that she just cost Gil his job. Finally, the Simpsons buy him a house in Scottsdale so he can keep his job. The episode ends with a family of Grumples arriving at the doorstep. Homer lets them in and Gil, the Simpsons and the Grumples continue happily singing their carols.