I have eight cats, but I always had one the hid

He came with his two litter mates. Every time I brought another cat home, more he hid. Under the counter, under a end table. Right now he stays under my bed. The dog was the last straw

Takes a whole other meaning about a monster under my bed

I can call him out carry him to the food and water. Then the litter pan. He eats fine. Physically he is fine, its all mental.
How do I give him confidence? He doesn't agree he can be out among the rest of us. He will a couple of days then he is back under the bed.
Mittens just needs a psychiatrist
He hates him name too. He has a harsh look to his face he hears his name.
Help Mittens come out from hiding.