Motherships are mighty vessels that were constructed centuries ago during the golden age of protoss expansion. They were intended to act as primary command ships to lead vast armadas of protoss explorers into the darkness of deep space and bring them safely home again. Those days are long gone, and the surviving motherships later became holy shrines to the protoss, representing an honored way of life and a part of the proud history of the protoss race.
t the heart of each mothership is a huge khaydarin crystal infused with an incredible amount of psionic energy. By tapping into this energy, a mothership can warp or crack the very fabric of space and time itself. The devastating power of a mothership can wipe out squadrons of enemy ships in the blink of an eye or lay waste to entire planets. As the golden age reached its apogee, the motherships were left in place as titanic monuments at the farthest reaches of protoss exploration. It was believed that their like would not be needed again.
After the loss of Aiur, however, the motherships were called back into service from the far corners of the galaxy. Now they are crewed not with mystics and historians, but with warriors. The oldest and most powerful weapons of the protoss have been awakened and are prepared to burn the galaxy to avenge the loss of the protoss homeworld.

StarCraft II