The Collaborative International Dictionary
Interrex \In"ter*rex`\, n.; pl. E. Interrexes, L. Interreges. [L., fr. inter between + rex king.] An interregent, or a regent.
Wiktionary
n. 1 (context history English) An official in Ancient Rome, who acted as single head of state during the interregnum between two consulates. 2 (context history English) An equivalent regent from the death of a Polish king till the election and enthronement of his successor. 3 (context figuratively English) A similar interim ruler, CEO etc.
Wikipedia
The Interrex (plural interreges) was literally a ruler "between kings" ( Latin inter reges) during the Roman Kingdom and the Roman Republic. He was in effect a short-term regent.
The office of interrex was supposedly created following the death of Rome's first king Romulus, and thus its origin is obscured by legend. The Senate of the Roman Kingdom was at first unable to choose a new king. For the purpose of continuing the government of the city, the senate, which then consisted of one hundred members, was divided into ten decuriae (groups of ten); and from each of these decuriae one senator was nominated as decurio. Each of the ten decuriones in succession held the regal power and its badges for five days as interrex; and if no king had been appointed at the expiration of fifty days, the rotation began anew. The period during which they exercised their power was called an interregnum, and on that occasion lasted for one year, after which Numa Pompilius was elected as the new king.
After the death of each subsequent king an interrex was appointed by the senate. His function was to call a meeting of the Comitia Curiata which would elect a new king.
Under the Republic, interreges were appointed to hold the comitia for the election of the consuls when the consuls, through civil commotion or other cause such as death, had been unable to do so during their year of office. Each interrex held the office for only five days, as under the kings. The comitia were, as a general rule, not held by the first interrex, who was originally the curio maximus, but more usually by the second or third; but in one instance we read of an eleventh, and in another of a fourteenth interrex. The comitia to elect the first consuls were held by Spurius Lucretius Tricipitinus as interrex was also called praefectus urbis. The interreges under the republic, at least from 482 BC, were elected by the senate from its whole body, and were not confined to the decem primi or ten chief senators as under the kings. Plebeians, however, were not admissible to this office; and consequently when the senate included plebeians, the patrician senators met together without the plebeian members to elect an interrex. For this reason, as well as on account of the influence which the interrex exerted in the election of the magistrates, we find that the tribunes of the plebs were strongly opposed to the appointment of an interrex. The interrex had jurisdictio.
Interreges continued to be appointed occasionally until the time of the Second Punic War. After that no interrex was appointed until the senate, by command of Sulla, named L. Valerius Flaccus to hold the comitia for his election as Dictator in 82 BC. In 55 BC another interrex was appointed to hold the comitia in which Pompey and Crassus were elected consuls. There were interreges in 53 and 52 BC; in 52 an interrex held the comitia in which Pompey was appointed sole consul.
The institution of interrex existed in the Crown of the Kingdom of Poland, whose ruling classes liked to view their Republic (Rzeczpospolita) or Commonwealth as an heir to Roman republican traditions. The Commonwealth's monarch holding a double title of the Two Nations King of Poland and Grand Duke of Lithuania entered upon their office by free election (wolna elekcja), which often led to a relatively long interregnum. Since 1572, the role of interrex traditionally fell to the Archbishop of Gniezno and Primate of Poland of the Roman Catholic Church. The Archbishop could nominate a replacement (traditionally he would choose the bishop of Kujawy).
The interrex would represent the country on the international scene and oversee the internal administration until a new king was elected. In special circumstances he could declare war and negotiate peace. He summoned and presided over the convocation sejm and the election sejm, the gathering of nobility that elected the king. He also announced the election of the king.
align=center colspan=3|Interreges of the Commonwealth |-align=center valign=top
Took the office of interrex in
Gave up the office of interrex in
Interrex
align=center|1572
align=center|1573
Jakub Uchański
align=center|1574
align=center|1575
Jakub Uchański (again)
align=center|1586
align=center|1587
Stanisław Karnkowski
align=center|1632
align=center|1632
Jan Wężyk
align=center|1648
align=center|1648
Maciej Łubieński
align=center|1668
align=center|1669
Mikołaj Prażmowski
align=center|1673
align=center|1674
Kazimierz Florian Czartoryski
align=center|1674
align=center|1674
illness and death of Kazimierz Florian Czartoryski led to him being replaced by the bishop of Kraków, Andrzej Trzebicki and bishop of Poznań, Stefan Wierzbowski
align=center|1696
align=center|1697
Michał Stefan Radziejowski
align=center|1704
align=center|1705
Michał Stefan Radziejowski (again)
align=center|1704
align=center|1705
Michał Stefan Radziejowski was stripped of his authority by the Pope and went into hiding. He was replaced by bishop of Poznań, Mikołaj Święcicki
align=center|1733
align=center|1734
Teodor Andrzej Potocki
align=center|1763
align=center|1764
Władysław Aleksander Łubieński
Usage examples of "interrex".
Fabius Vibulanus, interrex, presiding in the assembly, Aulus Cornelius Cossus, Lucius Furius Medullinus were elected consuls.
Titus Quintius Barbatus, the interrex, elects consuls Lucius Papirius Mugillanus, Lucius Sempronius Atratinus.
There was only one possible mode of expiation, and that was that the consular tribunes should resign office, the auspices to be taken entirely afresh, and an interrex appointed.
The consuls were attacked by the epidemic, so it was decided that the auspices should be taken afresh by an interrex.
In addition to this new law, and the consul's edict enforcing it, a resolution was passed by the senate ordering that whenever any one of them was manumitted and publicly declared to be free, the dictator, consul, interrex, censor or praetor for the time being should put the manumitter on his oath that he was not doing it for the purpose of altering his citizenship.