The person driving would be responsible for the damages. The person who rented the car may also be responsible under the terms of the rental agreement. You will need to review this agreement.
Assuming this accident took place in the State of Florida, the rental company owning the vehicle could be responsible for damages up to the statutory limit. However, since it appears from your question that the person driving the rental car was not authorized to do so, the rental company may not be liable, as there was no permission given to this driver to operate the vehicle. In Florida, the owner of the vehicle is responsible for any damages caused by a permissive user. If the unauthorized operator of the rental vehicle has their own insurance on another vehicle, that coverage would apply.
However, the automobile insurance company for the unauthorized driver rental vehicle, may deny coverage for the incident because he was not an authorized driver based on the terms of the rental agreement. Assuming, of course that he is insured, covergae will depend on the terms and conditions of the insurance policy for the unauthorized driver. The insurance carrier may take the position that this accident is not a covered event, making the driver of the vehicle personally responsible for any damages caused by this accident. The essential question will be : Did the driver of the rental vehicle believe that the individual that rented the vehicle have permission and/or authority from the rental agency to grant the unauthorized driver, permission to drive the vehicle?
