Who is covered for rental car?

The term for this is "authorized driver", and usually only the person who signs the contract is included (some agencies automatically include spouses at no extra charge). You can usually pay an additional one-time fee to add more people to the list of authorized drivers. Additional drivers will usually be required to be physically present when the contract is made, and produce a valid driver's license.

Anyone else who drives the car is considered unauthorized and this is considered a breach of contract for which you may be liable in the event of an accident.