Gordon Freeman

"Man of few words, huh?"

-Alyx Vance

Gordon Freeman is the silent protagonist of the Half-Life FPS series. Originally an MIT graduate working at a top-secret government facility known as Black Mesa, he inadvertently triggers an event known as a "Resonance Cascade", the long-term effect of which is drawing homicidal aliens to Earth in great numbers. It's then the job of this silent scientist to fight his way through the alien hordes single-handed despite having never used a weapon (other than a tennis-ball gun he built himself at age six), and to liberate the Earth from the insidious grip of forces quite possibly far beyond anyone's understanding.

As near as we know, Gordon Freeman has never spoken at least since the start of Half-Life 2, and quite possibly not at all since the Resonance Cascade (as quotes like the above evidence). The reason for this isn't clear; there is no evidence that he is incapable of doing so, such as a damaged voicebox, but the long and the short is that the Freeman does not talk. Causing Freeman to speak is thus a viable charge and in fact a rather serious one, due to his lack of established personality.