What's the legality in the USA to pay someone an annual salary to?
So long as do whatever you say doesn't involve committing a crime (including prostitution), and the person is free to exit the employment relationship, then you can definitely pay someone to move in with you and do your bidding. The tax situation can be complicated. A lot depends on whether this person is considered an employee or independent contractor. If an employee, you will be expected to withhold income tax and social security tax, AND you will have to pay the employer's share of social security tax. If contractor you don't do either of those things. Either way, the fact that you are providing housing may also be considered income for that person, if you're also providing food, likewise. If you're serious about having a live-in servant, you should consult a tax adviser for professional advice about the employee/contractor designation, as well as the treatment of the housing and food costs.