Though "NCIS" fans watched Pauley Perrette play Abby Sciuto for years, the forensic scientist was almost portrayed by Katee Sackhoff instead.

TVLine has learned that Sackhoff auditioned for Abby when casting for the role had just begun — but she had already tested for "Battlestar Galactica", too. Sackhoff was ultimately cast on BSG as Kara Thrace, and Perrette landed the "NCIS" gig instead.

https://tvline.com/lists/tv-actors-almost-played-different-roles/katee-sackhoff-ncis/