Buffy, the Vampire Slayer

Sarah Michelle Gellar was the only one to appear in all 145 episodes (including the unaired pilot). Alyson Hannigan appeared in all 144 of the regular episodes. Nicholas Brendon was only absent in 7x07.

Entertainment Weekly magazine named Buffy the number 3 character of all time, coming behind Homer Simpson and Harry Potter, in 2010.

There are just seven episodes in which no vampire appears. They are 'Witch', 'The Pack', 'Robot... You, Jane', 'The Puppet Show', 'Inca Mummy Girl', 'Living Conditions' and 'Fear Itself'. In the other ones, even when there are not vampire foes, there's always Angel or Spike. Or both.