4) Lisa Robin Kelly
Kelly played the pretty and ditzy older sister of Eric Forman on That 70s Show. She abruptly left the show in the third season, returned for a few episodes in the fifth season and then permanently in the sixth season. People were oblivious to her unpredictable appearances and only took notice when she was arrested for various DUI and assault charges. Sadly, Kelly died in a rehab facility after ingesting a cocktail of pills.