J is for Joyce Summers
Joyce Summers is Buffy and Dawn's mother, and she was never given much more of a backstory than that. Joyce and her husband Hank divorced not long after Buffy became the Slayer, and Joyce subsequently moved Buffy and herself to Sunnydale to start a new life, and where Joyce would own and operate an art gallery.
Joyce was ignorant of Buffy's status as Vampire Slayer for the first couple of years, finally learning the truth at the end of season 2 (although after Dawn appeared it seemed that Joyce (and Dawn) had learnt the truth a lot earlier).
Buffy: Open your eyes, Mom. What do you think has been going on for the past two years? The fights, the weird occurrences... how many times have you washed blood out of my clothing, and you still haven't figured it out?Joyce was one of the few characters on the show to have a natural death, dying of a brain tumour in season 5. This left Buffy alone to raise and protect Dawn.
Joyce was the maternal figure for the show. She played the visible, loving supportive mother to Xander's abusive, neglectful mother and Willow's absent one. She was caring, and looked out for the others, even welcoming Faith and Spike into the fold. But she was also absent from a lot of the story lines, and never a main character. I feel like there was a lot more to Joyce that we never got to see, and it would have been nice to have seen her relationship with Buffy explored a lot more.