US 60's sitcoms constantly used this ruse to stretch their shelflife/ratings. Here's my list, I'm sure you can think of others:
- "The Patty Duke Show" (inspired by Disney's "The Parent Trap" 1961)
- "The Flintstones" (Fred and Barney had doubles at different stages)
- "The Addams Family" Morticia had the nutbag relative, Ophelia, she had daisies growing in her hair, from memory, if she tried to pull one out, her knee bent upwards
- "The Munsters" with Herman's conniving brother, Charlie
- "The Beverly Hillbillies" Max Baer Jr (Jethro) frocked up as twin sis Jethrine. Inspired! Looking like Jack Lemon in "Some Like It Hot"
- "Bewitched" Samantha's sister, black-haired Sabrina trying to seduce the hapless Darrin
- "I Dream of Jeannie" - those dark wigs come in handy - Jeannie II, the wicked sister.
- "Gilligan's Island" had Gilligan and Ginger with doppelgangers. There were only 7 castaways on the island so you had to spicy it up somehow.