Gordon Freeman
The character is seen first as a theoretical physicist working at Black Mesa Research Facility and working in an experiment which accidentally opens an portal, releasing confused, harmful aliens into Black Mesa. In the first Half-Life, Gordon Freeman fights through the facility with other workers, fighting the aliens as well as a military unit sent in to stop the incident and silence any surviving witnesses. In the second game, Half-Life 2, Gordon is introduced to a military world years after the Black Mesa incident, along with a force known as the Combine that took over the world.