Doug Rattmann, also known as the "Rat Man", deserves more stamps. And if you don't know who he is, you need to play more Portal. And Portal 2. And read the incredibly gorgeous comic "Lab Rat", released by Valve. I won't spoil anything for you, but Doug Rattmann is the very definition of a tragic hero. And his sidekick is a weighted companion cube that talks to him. So he's got that going for him.
Also, if they ever made Portal into a movie, I think Rattmann should be played by Gary Oldman. Only he could pull off that degree of mental instability.