"One Life to Live" (1968-2012)
Multiple personalities are as much a soap opera standard as amnesia, evil twins and returning from the dead -- in "One Life to Live," for instance, main character Viki Lord (Erika Slezak) has struggled with DID throughout the decades. Caught between wanting to please her controlling, abusive millionaire dad Victor and to be herself, Viki developed the alternate personality of Niki Smith, a wild party girl who complicated issues by falling for Vinny Wolek (Antony Ponzini) despite Viki's being in love with reporter Joe Riley (Lee Patterson). While Viki was treated for her condition, Niki would pop up again and again to wreak havok on Viki's life over the years (though she did also come to the rescue), eventually joined by other alters that included 14-year-old male Tommy, the psychotic and murderous Tori and a version of Viki's father. Viki's daughter Jessica (Erin Torpey, later Bree Williamson) was released to have inherited her mother's condition, enabling the nutty storylines to continue across generations.
The producers of "Taxi" allowed Andy Kaufman to give the character of Latka Gravas different personalities to keep the comedian/performance artist from getting tired of always playing the same role, one inspired by his Foreign Man act. Latka, was an innocent, friendly and heavily accented immigrant from an unspecified country, but his alter ego Vic Ferrari, born from Latka's studying of radio DJs and Playboy magazines, was slick, a ladies' man and somehow spoke much better English. In the season four episode "Mr. Personalities," Latka is taken to a psychiatist after developing other alters, including that of the cowboy Arlo and the English Jeffrey, eventually taking on the personality of colleague Alex (Judd Hirsch), and offering up a deeper understanding of the man's life than Alex himself possesses. "Family Matters" character Steve Urkel (Jaleel White) had a similarly suave, smooth-talking alter ego -- Stefan Urquelle.
"Melrose Place" (1992-1999)
Marcia Cross's Dr. Kimberly Shaw was in multiple comas, attempted suicide more than once, stole a baby, had hallucinations, blew up a building and continually swore revenge on her enemies, including her scheming sometimes-love and sometimes-tormentor Michael Mancini (Thomas Calabro). So when she developed dissociative identity disorder in season four of the Aaron Spelling primetime soap, it was only the latest (literally) insane thing to happen to the character. The best thing about Kimberly's adventure in multiple personalities was that her initial alter, Betsy, a Bree Van de Kamp-style prim and perfect housewife who did the ironing, hosted tupperware parties (!) and would sooner set a sofa on fire than use it again after people have had sex on it -- also, she wanted to kill Michael, not a new urge on the show. Later, another alter, the cigar-smoking biker chick Rita, showed up ("Rita knows how to take care of her man"), and Kimberly attempted to get help from Dr. Peter Burns (Jack Wagner), only to be taken over by Betsy, who then tried to go Nurse Ratched on everyone.