ALYX VANCE: A brand new character in Halflife 2. She is the daughter of Eli Vance and acts as Gordon's sidekick. Her mother perished in the original incident at the Black Mesa compound and she now fights alongside you in some areas of Halflife 2.

BARNEY CALHOUN: Originally you know Barney from Black Mesa security, and then made an appearance in the expansion Blue Shift. Now hes here to help in City 17 to fight beside you.

ELI VANCE: Originally a Black Mesa scientist and now father to Alyx as well. He lost his leg in the original game before escaping from Black Mesa and will help guide you in Halflife 2.
THE G-MAN: This was a very mysterious character in the first Halflife. Now he's back, and our character Gordon has been working for him. He's put in enemies because he gave Gordon the ultimatum to join him or die. Obviously Gordon gave in.
GORDON FREEMAN: The main character of the game. You play this scientist that was the original star of Halflife. He was offered a deal from G-Man at the end of the first game to come work for him. Apparently he accepted and has now been working for G-Man over the past 15 years.
SCIENTISTS: You will be interacting mostly with Dr. Alex Kleiner (the man who originally got Gordon the job at Black Mesa). They will help provide valuable knowledge along your way in Halflife 2. This time they will also have unique skins so you can tell them apart better.