Sally Fletcher from Home and Away played by Kate Ritchie lasted a good 20 years; from 1988 - 2008. Kate started this role when she was 10 years old.
However Kate reprised her role as Sally for one season in 2013 making it her role for 25 years. Altogether she has appeared in 1775[1] episodes.
It should be noted that the show is still ongoing, and the character may return at any stage.