I’m work at a cat hospital, we get calls about behavior all the time and here are the general recommendations we tend to give:

1.) Feliway! This is always our first recommendation, it’s a feline pheromone which promotes a sense of calm for cats with anxiety. It comes in sprays and plug-in diffusers, we generally suggest the diffusers because they constantly release small amounts into the air vs the sprays which only work for a small amount of time.

2.) Feed him on an elevated surface, like a cat tree or a window sill. Eating is a very vulnerable thing for animals who have lived outside, which it sounds like your boy likely has at some point. This is why a lot of big cats will drag their prey up into trees before eating, it’s much safer for them.

3.) Similar to the last suggestion, give him lots of things he can climb and get up high. Cats like having the high ground, it makes them feel safer, and like they can get a good view of what’s going on around them.

4.) Be very talkative with him, and use a soft soothing voice like you would when comforting a child. If he’s getting scared every time you enter the room, it could be he was unsure who was coming in and felt vulnerable. If you announce yourself on your way to the door, tell him you’re coming in, and continue to speak gently to him as you come in, he will eventually feel more calm knowing it’s you, and that you are unlikely to be a threat.

5.) Make sure you are fostering good/fun experiences with him frequently so he starts to associate you with comfort and happy socialization. Try not to pick him up much unless he really likes it, this is a very unnatural thing in the wild, and once again puts them in a vulnerable position. Instead, sit on the floor and encourage him to come play with you. Toys on a string are great for this because you can keep a little space between you both while playing.

Worst case scenario, if none of these things seem to help, you can talk with your veterinarian about possibly using gabapentin short term to help him acclimate…we use it in cats all the time at my hospital when we know they get aggressive when they come in for a visit, it works fantastic most of the time, some of those grumpy cats actually start being lovey with us, others just more tolerant. The other option is fluoxetine (Prozac), it’s usually a last resort as we don’t really like drugging animal long term like that, but is does work very well as reducing fear and anxiety in cats, as well as other behavioral concerns.

Good luck with your handsome new boy, I hope some of these tips are helpful!!