Barney Calhoun is a playable character in Half-Life: Blue Shift, and a major character in Half-Life 2 as well as Episode One. Starting out as a security guard at Black Mesa Research Facility, he eventually joins the Lambda Resistance and works as a mole in the Combine Civil Protection Forces.
In Half-Life 2, Alyx Vance is a brilliant hacker and mechanic who is a close friend of Gordon Freeman. She helps Gordon by providing weapons and fighting alongside him. She owns a robot named “Dog”, which she built herself.
Gnome Chompski is a garden gnome who likes to make unlikely appearances in video games, including Half-Life 2, Left 4 Dead 2, and the Final Hours of Portal 2. As far as we can tell, there’s no relation to the famous linguist.
In the Portal games, Chell is essentially a lab rat for Aperture Science, performing tests under the supervision of the AI bot GLaDOS. It’s not long before Chell sees her chance to escape the testing facility using her portal gun.
In Team Fortress 2, the Scout is your typical messenger: quick, snarky, and a lot tougher than he appears. He likes to inflict damage with his baseball bat and escape before the opponent knows what hit him.