Sarah Kerrigan had insane psychic abilities and was thus forced into the Ghost program. She accidentally killed her own mother and incapacitated her father in the process. And we won’t even go into the traumatic path that led to her transformation (it included losing her lover to murder).
Honestly, if she had ended up becoming a meth head hiding on some moon-rock , we wouldn’t have blamed her. Instead, though, she was captured and re-emerged as an infested Zerg Queen, a shell of her former self. She yearned to return to humanity, which is tough after you’ve slaughtered millions. It’s a tragic tale of nearly Shakespearean proportions, which is why she ranks so high on our list.