Back in the day, Willow was a total nutjob. She was fine with us, never scratched us or attacked us, but strangers were a different issue. Anyone who came through the front door would be stalked by Willow, but Willow would appear friendly and sweet, so the stranger would inevidibly reach to pet her. His hand would meet with claws, not fur. One plumber got cornered in the bathroom by Willow, and one repairwoman had Willow leap off a couch, launch onto her chest, then leap away and run off. When she was spayed, the vet techs had to gas her in her cage because she wouldn't let them anywhere near her, and we had to come around to the back room to bring her home because, again, she wouldn't let the techs near her. And once, Willow had gotten outside and stayed out for 3 days, but when she finally came back, she was NASTY! We didn't know how she'd gotten out, but shortly after eating a meal after coming back inside, I followed her downstairs and up to a window, one with a hole in the screen that we hadn't seen before. When I grabbed Willow away from the hole, put her on the ground, shut the window, and turned around, Willow screamed and chased me into a corner. That was the worst we'd ever seen Willow (though we understood it was because of the high of living in the "wilderness" for 3 days. It took her 3 weeks to return to normal).
But you know what changed? When Willow was 2, we brought in a 2nd kitty, little 4 week old orphaned Buffy. Due to Willow's nature, we were skeptical about how she would take to Buffy, but after just a week, Willow made the first move towards being friends, and from there on out, Willow was Buffy's surrogate mother. She took over all the mother duties and over time, she really started to mellow out. Nowadays, a stranger can walk into the house and she won't even care, though she'll still hiss and scratch at a stranger who tries to pet her. She's calmed down and is much nicer, and seems to like being able to just sit back and relax and watch Buffy (and the more recent addition, Molly) get into trouble. I think most of Willow's problems stemmed from fear and stress (and lack of socialization, since we got her as a 6 week old and she never left the house). She's still skittish, but having a fellow cat-buddy has really calmed her down, given her a sense of security.