Buster, a black and white tuxedo male, was about 4 years old when we adopted him in August 1997.  He was raised by a dear coworker of mine named Bette. He was her sole companion and when she died at 80+ years, we took him in because the relatives weren't sure what to do with him, and Bette had expressed the opinion early on that he would need to be put to sleep when she died.

Bette's main concern about Buster had been that he would never adapt to another household. He was a "hider" -- whenever company came to visit, he was nowhere to be found. He was also a picky eater (I don't think he had ever eaten canned or dry cat food, just turkey, chicken, and tuna - essentially whatever Bette was fixing for dinner), and was only used to having one person in his life.  As near as I could tell, he'd never met another cat.

The first 2 days Buster was here, he hid under the bed (actually, inside the box springs). He refused to eat, and would only hiss if I tried to touch him. The second night, I spent 2 hours lying prone on the floor, talking and cooing to him. Eventually, he climbed out of the bed and walked over to me - and, quite literally, "furred" me, pushing his face against mine until I could barely breathe from all the cat fur.  He also took the opportunity to tell me his entire life story; I think he talked non-stop for 15 minutes.

He clearly needed the litter box, so I picked him up and carried him into the bathroom. He used "the facilities" then dashed back under the bed.

Next day I arranged the den for him - put a basket under the chair, and covered the chair with a towel so he could hide. New litterbox, cat dishes, etc., were readily available in the room for him. We closed the door, and I'd go visit with him every few hours. By the next evening, we were keeping the den door open for longer and longer periods of time.

Shortly after that,  Libby essentially moved into his room (the den) with him, took over his basket, and taught him the finer points of cat socialization and playing. For a while, he had a definite "angst" about the other boys and Su-Su, and he prefered to stay in his den and howl (just like a dog!) for attention.  Eventually, he became comfortable in moving between the den, bathroom, and bedroom.

He became a happy, healthy, contented cat, fully integrated with the rest of the household. He held his own ground with the boys,  staked out several spaces in the house as his own, and no longer hid when visitors arrived; he even let the Schwan Delivery Man (who came over for 15 minutes every 2 weeks) pet him.

Buster typically followed me into various rooms - unless the door was closed tightly, he'd figure out a way to open it.  He had also been known to spend hours sleeping on one arm while I was at the computer.