4. Andrea (The Walking Dead)
When we were first introduced to Andrea, she was a tough-talking, Walker-slaying power woman. Ravaged by the death of her sister, she hardened to become more or less the female equivalent of Rick and Daryl in the main group of survivors. Unfortunately for her, she was slowly edged out of that group due to her constant fraternising with Shane, until she was (accidentally, admittedly) abandoned on the Greene farm and left to fend for herself, via Michonne. She fell even further when she was taken in by The Governor, and quickly became not only a close ally of his, but also his lover, all despite the fact that the man was an utter psychopath. She'd flipped totally to naive and irritating from the strong character she'd once been. The culmination of season three saw her presented with the opportunity to redeem herself; she leaves Woodbury to rejoin her original group at the prison, but is easily captured by The Governor and locked in a torture chamber, wherein she is bitten by the recently walker-fied Milton, ultimately shooting herself by Michonne's side. This is not what we expected. Andrea was supposed to be a prominent figure, rising from the ashes to help her friends in their war with Woodbury. Instead she was picked off with the minimum of effort on the part of her adversaries. Whilst it made for extremely emotional viewing, her death was simply not in the script we had imagined, and despite her fall from grace, she left a huge hole in the group, leaving Maggie as (at the time) the only particularly strong female character entirely trusted by the survivors.