He ended up in the shelter when the son didn't want him. He was in and out of the shelter and by the time I arrived he as very traumatized. When cats get traumatized they tend to quit eating. He was very emaciated. For multiple reasons it was a major decision to take him in. I feel like I made the right decision.
On the first day home he didn't immediately hide and he started to eat ravenously. I thought that was a very good sign. It took about ten days for him to regain his strength and stop being lethargic. He is steadily gaining back his weight. For his size he should get back up to 20 pounds. The other cats aren't so sure about the whole thing, but there haven't been any confrontations. All in all I am very pleased with the progress.
He has decided I am now his human. Everything tells me he was accustomed to a great deal of human interaction, especially in the petting department. He has now taken to sleeping with me. It's like sleeping with a 20 pound sack of potatoes because, unlike the other cats, he doesn't scoot over very easily. He has a mild purr, but a gigantic meow. I am glad I brought him home.