Star Trek Voyager - Captain Janeway
Unaired Pilot portrayed by: Geneviève Bujold
Officially portrayed by: Kate Mulgrew
Reason for recast: Bujold was originally cast as Nicole Janeway, having never done tv before Bujold was not used to everything that went into a tv series and the producers knew that it would not work out so Bujold walked away from the part before they tried to force her out. Bujold also had a hard time connecting with the cast and played Janeway as a very cold Captain. Bujold requested the character be named Nicole but after she left, they changed it to the now iconic Kathryn Janeway.
Gilmore Girls - Dean
Unaired Pilot portrayed by: Nathan Wetherington
Officially portrayed by: Jared Padalecki
Reason for recast: Unknown.
Nathan Wetheringtons portrayl of Dean differed from Jared. Nathan portrayed Dean as more unsure of him and a bit more of a creep.
Desperate Housewives - Mary Alice Young
Unaired Pilot portrayed by: Sheryl Lee
Officially portrayed by: Brenda Strong
Reason for recast: After filming the pilot, the producers felt that Sheryl was not right for the role.
Mary Alice Young was meant to be a sympathetic, nurturing character, something that Sheryl wasnt able to bring to the role. Her version of Mary Alice was a lot more mysterious and cold.
Buffy The Vampire Slayer - Willow
Unaired Pilot portrayed by: Riff Regan
Officially portrayed by: Alyson Hannigan
Reason for recast: Producers felt like Riff was not right for the part and knew they would recast for the official pilot. Riff played Willow as to insecure and was not able to bring the character to life like Alyson did. Casting director talks recasting Willow Here
Desperate Housewives - John
Unaired Pilot portrayed by: Kyle Searles
Officially portrayed by: Jesse Metcalf
Reason for recast: Producers were not feeling the chemistry between Searles and Eva Longoria, who was supposed to be having an affair with her teenage gardener. They also wanted the character to have more sexual appeal to help justify why Gabrielle would have an affair with John.
Charmed - Phoebe Halliwell
Unaired Pilot portrayed by: Lori Rom
Officially portrayed by: Alyssa Milano
Reason for recast: It is rumored that Lori left of her own accord due to her religious beliefs ending up making her realize that she could not star in a show about witches.
Lori's version of Phoebe differed greatly from Alyssas with Lori's Phoebe being an a lot more mature younger sister compared to Alyssa's more playful and immature version.
Mighty Morphin Power Rangers - Trini
Unaired Pilot portrayed by: Audri Dubois
Officially portrayed by: Thuy Trang
Reason for recast: Audri Dubois was the original Yellow Ranger before the semi controversial casting of Thuy Trang as the Yellow Ranger. According to Walter Jones, Audri asked for more money which is practically a big no no with Saban. She was fired and recast. Audri's version of Trini was a lot more tomboyish then Thuys version. Dubois states that originally Trini was supposed to have no martial arts background, timid, and be the heart of the group before the producers figured out that she was a 3rd degree blackout.
Married With Children - Kelly and Bud Bundy
Unaired Pilot portrayed by: Tina Caspary and Hunter Carson
Officially portrayed by: Christina Applegate and David Faustino
Reason for recast: Ed O'neil did not feel any chemistry with the first round of kids so they recast the roles and the rest is history.
Source: Me, myself, my memory + 1 2 3 4 5 6 7 8 9 10 11