Gary, a scientist who worked for an undisclosed science facility, that could be best described as Black Mesa and Aperture Science combined into one. But that was before the apocalypse came around. But it doesn't help that he indirectly caused it. During an experiment, a critical failure while working with a portal had creatures coming out of it. They tried sending armed guards to dispatch them, but it didn't work, and now, the apocalypse is happening, those same creatures roaming around, waiting for they're next kill.