Dr. Ariel Hanson. Why? A reason that will require explanation. She went and experimented on herself to try and find a cure for the Zerg virus. She does this if you pick a particular option for a particular mission. Namely, the mission regarding a new colony settled by her people on a planet called Haven. The colony went dark, and it's revealed that a Zerg infestation is on its way.
When you arrive the Protoss are already there, ready to take out the colony themselves. Your options are to either support the Protoss, by telling them to stand down and let you handle the Zerg infestation, because it is human business after all. This can lead to you having to destroy some of the colonies, and humans, that end up infested. Or, you can support Dr. Hanson, and fight against the Protoss to prevent them from destroying the human colonies.
I went with the Protoss option, because I wanted the highest chance of saving the humans. Apparently, during the mission, Dr. Hanson locked herself in the laboratory, all pissed off at me because I picked to deal with the infestation myself.
Interestingly enough, I managed to save all of the colonists. I warded off every single potential infestation with a large force of Vikings, and managed to take care of the Zerg territory with a bunch of Marines, Marauders, Goliaths, and probably some other heavy ground forces. So Dr. Hanson was pissed for no reason at all. But she was still pissed, and experimented on herself with the Zerg virus. Needless to say, she got Zergified, and she had to be killed. But still, I managed to do exactly what she wanted me to do, saving the colonists, and she still got herself killed.
