While much of the show is live action, alien characters whom producers claim would be to hard to portray by a person in a costume, such as Urdnot Wrex, were created using advanced three-dimensional computer animation, and voiced by the same individuals who had voiced them in the games.
The protagonist of Mass Effect is a male Commander Shepard and the default player in the game series, the earthborn war hero, John Shepard, who is portrayed by Matthew Fox. While in the game series, Shepard's behavior is determined by the choices made by the player, the television series' John Shepard is for the most part, Paragon in his morality. John Shepard's personality and history was intended so that he would appeal to most audiences as "a good man with a pure heart, despite the odds due to his rough childhood."
Shepard's static love interest throughout the series is Gunnery Chief Ashley Williams, whom he affectionately addresses as "Ash", and is played by CanadianactressErica Cerra. Ashley does not appear in season two of Mass Effect, in accordance with the pre-established storyline, however, she does make a comeback in the third and final season. Staff Lieutenant Kaidan Alenko, a close friend of Shepard's who appears only in the first season due to his untimely death on Virmire, is played by Rapheal Sbarge, his voice actor in the games. Captain, later Admiral David Anderson, the previous captain of the SSV Normandy, and an old friend of Shepard's, is played by Keith David.