Dr. Chakwas

When Shepard decided to stop being part of the world and to undergo cryosleep, she knew that she never wanted to be awakened again. She had lost everyone that ever mattered to her in an expedition gone wrong. But the unthinkable happened, the human race had encountered another intelligent race and things hadn't gone the way anyone expected.

Now Naval Command is in need of Shepard's help whether she wants to give it or not.