Viceroy

The term Viceroy has two distinct meanings, depending on the faction in which it is used.

Regional Viceroy (Federation)
The elected head of a region within a Federation planet. not be confused with the Imperial Viceroy,.

Imperial Viceroy
The second-in-command of the Imperium of Humanity, appointed by the Emperor, or failing that, by the Imperial Council of Regents, if the Emperor is a minor or unable to assume his duties.