Nowhere in the US Constitution does it forbid fictional characters to be elected to public office.
The only requirement is that "citizens must be born in the US".
well, according to the wiki:
Therefore, he is eligibility for candidacy is valid.Gordon is a native of Seattle who exhibited an early interest in theoretical physics, especially quantum mechanics and the theory of general relativity. His childhood heroes were Albert Einstein, Stephen Hawking, and Richard Feynman. After observing a series of teleportation experiments conducted by the Institute for Experimental Physics at the University of Innsbruck, Innsbruck, Austria, the transmission of matter became Gordon's obsession. Gordon has no known dependents. He graduated from MIT with a Ph.D. degree in Theoretical Physics.
Gordon freeman for president!!