5. Rita (Dexter)
Rita Bennett was the quiet, suffering in silence with the occasional angry outburst girlfriend and later wife of Dexter Morgan, eponymous "hero" of the Dexter series. She survived an abusive marriage to her previous husband and father of her two children before settling with Dexter, and unknowingly to Miami's favourite serial killer, she got under his skin. Though she may have become extremely annoying in places, Rita was genuinely seen as a key aspect in how the show functioned she almost provided the ying to Dexter's yang, and actually made him a complete and, at least on surface level, functioning person. Furthermore, despite the suggested threats made towards her throughout her time in the series, you always felt that she was safe, because...y'know, her husband kills hundreds of bad guys and stuff. And that's exactly why viewers were left reeling at the end of the season four finale, where a mistakenly victorious-feeling Dexter returns home from finally killing The Trinity Killer, only to discover the body of his wife in a pool of her own blood in the bath tub, baby Harrison sat crying nearby. One of the trademarks of the show was an ability to produce a rising ominous feeling of what's to come, and though some of us may have expected Rita's death, that still didn't change the fact that whenever her demise would come would completely shake the foundation of the show, particularly on how Dexter would react to such brutality taken against him. The removal of Rita removed the calm side of Dexter that we wouldn't expect to have been unleashed until the show's later series, not halfway through the show's lifetime.