Terrans
The Terrans are the human colonists that find themselves in a war waged between Protoss and the Zerg, In this war, the Terrans are in a constant struggle for survival, while also dealing with civil wars. To survive the war, they are involved in alliances with the Protoss. They are technologically advanced and are slowly becoming a powerful race.
Originally, they were outlaws casted out on settler ships to a colony world. When the navigation computer of these ships shut off, they became stuck into a stasis for 31 years. They were scattered on three different colonies: Umoja, Tarsonis and Moria. Soon they reunited and formed a powerful Terran Confederacy.
Terrans have an average power, are very efficient if good micromanagement is employed and their building method is only moderately efficient. If the forces aren't prepared, these can be easily overwhelmed by Zerg. The The Space Construction Vehicle has more health than other units and repairs mechanical units as well as all buildings. Biological units are healed by the Medic, while also being able to blind enemies with its Optic Flare.
Strengths:
Mobility, great defense, build anywhere, cloaking, versatility, Marines, strong through whole tech-tree, easy to learn, instant cloak detection, ability to repair buildings and most units.
Weaknesses:
Tendency to "turtle", need lots of space, require active scouting, require micromanagement for special abilities, vulnerable to Dark Swarm, buildings burn up when highly damaged.