Nihlus Kryik

Nihlus is a Council's Spectre, and was put in charge of watching Shepard on his mission on Eden Prime to see if Shepard was ready for Spectre status himself. But as he goes ahead on the mission, he is assassinated by Saren, the main villain of the first Mass Effect. Nihlus although very powerful and having a good sense of justice (he is a spectre after all) easily dropped his guard to his friend, and that was his demise. (Of course it's not his fault his friend got indoctrinated) Nihlus was also mentioned to have once been in a cat and mouse fight with Samara, who was forced to fight him because of her code, but he escaped by making it so she had to choose between killing him, and rescuining a civilian, and Samara obviously chose to save the civilian.