19. Dee Was Originally Played By Another Actress
Though it's incredibly difficult to imagine anyone but Kaitlin Olson playing the role of Dee Reynolds, the part was originally intended for actress Jordan Reid, who played Dee in the pilot and was at the time the girlfriend of Mac himself, Rob McElhenney.
But when FX was planning to take the pilot to series, Reid broke up with McElhenney, which according to her own account led to her being fired from the show and ultimately replaced with Olson, who would of course later become McElhenney's wife.
Though the jury remains out on the veracity of Reid's entire story - who claims she was edged out of a show she helped co-create - it's nevertheless fascinating to consider that the Dee fans know and love almost never came to be.