Sarah Kerrigan. There is so much artwork out of Sarah Kerrigan, both official and fan made, that I really had to cherry pick for this, since I really don't want these to be just a 'look what I found on google image' type of thing.
Kerrigan during the Battle of New Gettysburg
Kerrigan was the first of the named Ghosts, and really was the character that gave a shape to what Ghosts were supposed to be. She really epitomizes what's good about the Terran faction, and by extension, humanity in general. She's been dealt a crap hand, but she plays it the best she can, and she sticks by her friends.
De-infested Kerrigan as she appears in "Heart Of The Swarm"
Captured by the hideous alien Zerg during the Battle of New Gettysburg on Tarsonis, Kerrigan is betrayed and abandoned to her fate by Arcturus Mengsk, setting the stage for greater conflicts to come.