Worker

From The StarCraft 2 Wiki

Workers are the most basic unit of each race, perhaps with the exception of the Zerg, which has the Larvae. These "workers" has in common that they can harvest resources in the form of minerals and gas to the base, and to "build" structures.

The worker units are:

• Protoss - Probe
• Terran - SCV & Mule (only harvesting)
• Zerg - Drone