Sidh rulers traditionally hold the title of the Emperor of Sidhae. It is the highest office of the Imperium and commands near-godlike reverence and authority.
Although also denoting a type of monarch in Sidh language, the primary context in which "Imperator" is used in Sidh language is meant to denote someone commanding imperium, i.e., the authority to command, in a similar sense as used by Romans. Sidh language has different terms for varying degrees of authority, imperium being the highest, hence the holder of that authority being titled Imperator.
The following paragraph of the Statutes defines the role of the Emperor of Sidhae:
The sovereign ruler of the Imperium, henceforth referred to as the Imperator (Emperor) of Sidhae, shall be elected for life in a general election held by eligible citizens. The candidacy for Imperatorship shall be open to any eligible citizen. The Imperator shall command supreme executive, legislative and judicial authority limited only by provisions specified in the Imperial Statutes.
Although the Statutes specify the Emperor to be an elected official with dictatorial powers in all but name, thus far none of the Sidh leaders has actually attained power by means of a general election. The original Emperor was granted the title as the default leader of the Sidhae, his daughter the current Empress in turn securing her office after a lengthy civil war. Due to the Sidh reverence for their emperors and a general culture of conformity and submission to authority, neither case ever prompted the Sidh people to demand an election.
Ave Imperator (Hail the Emperor) is the customary salute used as the opening phrase in all official documents and public announcements in the Imperium. Although Ave Imperatrix is in principle equally acceptable, it is not used in formal setting and more commonly encountered in personal interactions under semi-formal circumstances due to the Empress distancing herself from the cult of personality of her father.