All agents, by an express undertaking to that effect, may render themselves individually liable. Every agent exceeding the scope of his authority shall be individually liable to the person with whom he deals; so, also, for his own tortious act, whether acting by command of his principal or not, he shall be responsible; for the negligence of his underservant, employed by him in behalf of his principal, he shall not be responsible.
OCGA § 10-6-85