Carries sister in King of Queens, mentioned in first episode, never seen/heard of again.
Tims brother in Not Going Out. Mentioned in episode 2 of series 1, never again and then he has a sister.
Tim then goes to Germany for work and is never mentioned by Lee & Lucy again, strange considering he is the kids uncle.
Many years back in Grange Hill, I’m thinking mid-90s, there was a character called Anna. She was a bit gobby and obnoxious. They showed part of her home life with disinterested parents. The end of the show that year was the third year going on a choir trip to Germany, when they came back she was just stood alone in the schoolyard after everyone else had been collected. Never mentioned in the next series.
Anita from Band of Gold, major character in the first two series. I know it was re-tooled and became ‘Gold’ for series 3 but it was still set in the same area and the women had been through a few murders/attempted murders and so much together but she was never mentioned.
Even for most of these a throwaway line like “Oh, she’s really enjoying living in Leeds” or “Mum & Dad loved their holiday with Tim”. It’s weird to just act like these people never existed, especially those that are related to other characters!
In books:
Miss Simms from the ‘Agatha Raisin’ series. Quite a main character in the first few books then never written about/mentioned again.