StarCraft

Starcraft is, in my opinion, one of the most important games in the industry. It was released in 1998 by Blizzard, it was the warcraft series "successor".
This game brings you a whole warlike world in which there are three races fighting for the universe supremacy: Terrans, Protoss and Zergs.

Terrans:
Humans. They are the most balanced race in the game, they are not as slow like the protoss, but neither as fast like the zergs.
Protoss:
Aliens. They've got the more powerful technology. Protoss are the strongest but the slowest too.
Zergs:
Aliens. They're the fastest race but their units are weak, they are known for attack in mass.

The game system is similar to every RTS game, you've got to get resources in order to build units and beat up your enemies.