Saren Arterius

Saren Arterius is the main villain of Mass Effect'. He is a turian veteran member of the Spectres, the top operatives of the Citadel Council, who has always been known to be very brutal and ruthless, having little regard for life, and hates humanity, thinking that they should be lower in the hierarchy of galactic society.

Prior to the events of the game, Saren met Sovereign, who is a Reaper, gigantic evil robots that terrorized the galaxy millennia ago, and started working with him hoping to overthrow humanity and also save the current life of the galaxy from the Reaper invasion, by aiding in said invasion, therefore proving lesser beings such as himself worthy to be spared. However, Saren eventually starts succumbing to the "Indoctrination" brainwashing effect of the Reapers and becomes Sovereign's obedient servant. Eventually, Saren is turned into a cyborg by Sovereign using his advanced Reaper technology.

During the game, Saren is searching for "The Conduit", an ancient relay device that can open a portal to the Citadel big enough for Sovereign to enter through. The final confrontation between Saren and Commander Shepard takes place beneath the planet Ilos, where the Conduit is located. Here, it is possible to convince Saren to realize he is being tricked and kill himself to delay the invasion, otherwise you have to fight him on his hover platform. Either way, after he dies his body is reanimated by Sovereign for the final battle, and shortly after that is destroyed Sovereign himself is killed by the starship fleet.