5. Mr House - Fallout: New Vegas
The last best hope for humanity, and your selfish desires to gain power or wealth cost us his mind. OK so I should clarify, Mr House isn't inherently bad, in fact he is probably the most moral person in New Vegas. When you first arrive after being shot in the face out on the wastes of the Mojave he is the one to welcome you and inform you of the situation. While initially he appears to just be a computer program you soon find out he is actually being kept alive through machines in a germ free environment so his body would not deteriorate. After going and taking the Platinum chip back from Benny, by any means necessary, you encounter the Yes Man, a reprogrammed securitron robot who was helping Benny with his plans to take over the strip. There begins a road of deception and betrayal - should you choose that - in which you fight your way into Mr House's tower and reach his inner sanctum. After busting in you find that the gentlemanly voice you've been hearing looks worse than a Ghoul after a hot day at Vault 87. When you unseal the chamber - and I know you did - he berates you for taking this choice, saying that it is you who have condemned humanity. He's not wrong either. In killing him you pretty much lose the wealth of knowledge and experience which would have benefited mankind for centuries to come and with you as his protege he was pretty much giving you the world. Killing Mr House is a dastardly deed and you should feel more than just shame for committing this heinous act.