The character played by Sasha Alexander "Kate" was killed by Ari the Israeli terrorist. Her role wouldn't be played by anyone but a new character by the name Ziva David a Mossad agent joins Gibbs team. The character is played by Cote de Pablo
She has not left, therefore she does not need replacing
Cote de Pablo as officer Ziva David (NCIS/Mossad liaison officer) in seasons 3 to 6, then probationary agent/ special agent Ziva David in seasons 7 to 11.
Ziva David
It depends on which season you are talking about; in season 1 and 2 it it is just Gibbs, DiNozzo, Kate, Ducky, Abby and Tom Morrow as director in season 2 we bring in McGee, in season 3 Kate and Tom go and Ziva replaces Kate and Jenny Shepard replaces Tom in in season 6 Leon Vance replaces Jenny Shepard as director . Then Ziva leaves and Ellie comes
Washington DC
No. Kate was just played by one person - Sasha Alexander
Todd
We never found out on the show.
It depends on which season you are talking about; in season 1 and 2 it it is just Gibbs, DiNozzo, Kate, Ducky, Abby and Tom Morrow as director in season 2 we bring in McGee, in season 3 Kate and Tom go and Ziva replaces Kate and Jenny Shepard replaces Tom in in season 6 Leon Vance replaces Jenny Shepard as director . Then Ziva leaves and Ellie comes
No
No. She died.
Washington DC
No. Kate was just played by one person - Sasha Alexander
Todd
Gibbs and Gearld
We never found out on the show.
Wendy Makkena
She was awarded the Presidential Medal of Freedom posthumously
The episode mentioned above is Bete Noir, which was aired in Season One of NCIS.
Kate Todd is played by Sasha Alexander, who left the season for personal reasons. Her character, Kate, is an ex-Secret Service agent who was invited to join NCIS by Agent Gibbs after she disobeyed a superior. She did not leave for personal reasons, she died, shot by Ari, Ziva's half-brother.