A priest who normally represents the Bishop in many different things around the diocese. Just like the Parochial Vicar represents the Pastor around the parish.
Think of the Vicar General as the bishop’s prime minister, vice president, or deputy sherrif.
Also, in many cases the Vicar General is himself a consecrated bishop. If a diocese has an aux. bishop, he is the logical choice for vicar general (I’m not sure if it’s obligatory or not). In the case of a coadjutor bishop (right of automatic succession when the reigning bishop retires or dies, like a vice president) he is the Vicar General automatically under canon law. Here in the Archdiocese of Vancouver the Holy Father recently sent us the Most. Rev. Michael Miller, formerly the Secretary for Catholic Education in the Curia, as our new Coadjutor Archbishop. Until the reigning Archbishop of Vancouver retires, Archbishop Micahel Miller will serve as Vancouver’s Vicar General.