Who is an Auxiliary Bishop?
The 1983 Code of Canon Law stipulates that if the pastoral need of a diocese requires it, the diocesan bishop could request the Pope to appoint for him one or more auxiliary bishops who will assist him in the entire governance of the diocese, and who takes his place when he is absent (Canon 405§2). The whole pastoral initiative of appointing an auxiliary bishop comes from the diocesan Bishop. Such pastoral considerations as the size of the diocese, the large number of Catholics or other pastoral concerns may move a diocesan bishop to seek the appointment of an auxiliary bishop. Canons 403 § 1 and 2 differentiate between two types of auxiliary bishops: the simple auxiliary bishop (§1) and an auxiliary bishop with special faculties. Canon 403 § 1 makes it explicitly clear that an auxiliary bishop has no right of succession if the See becomes vacant. Only the coadjutor bishop (Canon 403 § 3) has the right of succession. An auxiliary bishop takes possession of his office when he shows his apostolic letter of appointment to the diocesan bishop, in the presence of the chancellor of the curia, who makes a record of the fact (Canon 404§2). The auxiliary bishop is the immediate collaborator of the diocesan bishop (Canon 407§2). He is a fully ordained bishop who shares in the threefold function of teaching sanctifying and governing, but the diocesan bishop is the key decisional figure of his diocese.  On the 25 of May, Pope Francis appointed Ernest Obodo as the Auxiliary Bishop of Enugu, to help Bishop Callistus Valentine Chukwuma Onaga in his administration of the Diocese of Enugu. This is the first time that Enugu is having an auxiliary bishop.
 James A. Coriden et al, The Code of Canon Law, A Text and Commentary, London, Geoffery Chapman, 1999, p.339