Zeratul

Zeratul is a dark templar prelate and one of the main Protoss protagonists. This character is voiced by Jack Ritschel in StarCraft and it's expansion set, and by Fred Tatasciore in all parts of StarCraft II.

Starcraft and Brood War
A s a renowned psionic warrior and assassin, Zeratul is somewhat secretive and calculating, but is nevertheless honorable and loyal to his species. He teaches Tassadar how to use dark templar energies and facilitates the final attack on the Overmind by slaying several cerebrates. Following the death of the Overmind, Zeratul tries to put in motion the reunification of the Khalai survivors with the wayward dark templar and unmask the secrets of Samir Duran's experiments.

Starcraft II
After Duran revealed he had been breeding Protoss-Zerg hybrids for a greater master, Zeratul set out to find Duran's master and his plan, which encompasses all of his activities. In Wings of Liberty, he gives Jim Raynor a crystal with his memories to emphasize the importance of the latter's mission to de-infest Kerrigan. In Heart of the Swarm, he guides Kerrigan to Zerus, the original home of the Zerg, and encourages her to re-infest herself so she can stop Amon, a fallen Xel'naga who is revealed to be the master of Duran and seeks to destroy all life in the Korpulu Sector and remold it in his image. Zeratul will also feature in the events of Legacy of the Void (originally believed to be the central character, the actual protagonist of the story is Artanis).

Behind the scenes
Zeratul was created by Blizzard Entertainment's Chris Metzen, with concept art produced by other Blizzard artists such as Samwise Didier. Chris Metzen mentioned that Ritschel passed away sometime during the development of the game, and thus Fred Tatasciore has taken over as the new voice actor. Tatasciore described Zeratul as an incredible character, a "Darth Vader" who invests so much in the survival of things, and one of the best characters he has ever played. GameSpot described all the characters in StarCraft as "three-dimensional, full of personality and complexity", and then continued to comment: "Yet even among this star-studded cast, it is Zeratul who stands out as the most noble of heroes, although he is shrouded in a cloak of mystery and aloofness".