How to stop my male cat from being a bully?

Try a Feliway diffuser. Feliway is a pheromone that only cats can smell. It has a calming effect, however; it does not work on all cats. Try it for 2 months before deciding it doesn't work. If you have a large house or more than one level, you will want one for each level or each end of the house. This is a good idea for multiple cat households. It can help cats get along.