The Centauri Republic is governed from a capital city on Centauri Prime. The government appears to be a constitutional monarchy, with a senate-like governing body called the "Centarum" and a semi-hereditary Emperor. The highest officer of the Centarum is the Prime Minister.
One function of the Centarum is to elect/appoint the Republic’s Emperor. The Emperor wields considerable political authority in the Republic, serving as head of state, head of government, and commander-in-chief of the armed forces. The exact restrictions on the Emperor’s powers aren’t clear; the Emperor seems to wield most of the political power in the Centauri Republic, but the Centarum can overrule the Emperor’s decisions in unspecified circumstances. While the Centarum often appoints a related "heir" from the past Emperor's family, there is no indication that this is a requirement (although this is difficult to say for sure, the last three Emperors – Turhan, Cartagia, and Mollari – left no heirs of the body).
Four individuals have held the office of Emperor over the course of the Babylon 5 series. Emperor Turhan held the position until 2259, when he suffered a fatal heart attack while visiting Babylon 5. He was succeeded by his nephew Cartagia, who ruled until Londo Mollari and Vir Cotto assassinated him in 2261. A Regent held the throne for a period of months before Londo Mollari became Emperor in 2262. Vir Cotto succeeded Mollari as Emperor sometime before 2281, but the exact time of the change is unclear.
Three individuals have held the office of Prime Minister in the series. Prime Minister Malachi held the position while Turhan was Emperor; he was assassinated by agents of Lord Refa when Turhan died, and Refa became Prime Minister. Londo Mollari became Prime Minister after the death of Emperor Cartagia and held the office until he became Emperor himself.
The Centauri Republic was known to be in control of 12 worlds in 2258, but the extent of their territory fluctuated over the next four years as they fought wars against the Narn Regime, members of the League of Non-Aligned Worlds, and -- later -- members of the Interstellar Alliance. For example, the Narn Regime surrendered to them unconditionally in late 2259, giving them at least nominal control of all Narn territory, but they gave up at least some of that territory (Narn itself, if nothing else) in 2261. The extent of their territory in 2262 and later is unknown. Worlds known to have been under Centauri control during the series include Ragesh III and Gorash VII.
Centauri share the bipedal humanoid form common to all of the Young Races; this common basic body type may be a product of First One interference in the distant past.
Centauri are so similar to Humans at a glance that they claimed Humans were a long-lost branch of their race when first encountered. Their only visible distinction from humans is the pattern of their hair growth. Subsequent encounters, however, showed that Centauri are biologically much different from humans on the inside.
Centauri males are known to have seven genitalia, some of which are surprisingly long and prehensile. Londo was so dextrous with one of his appendages that he was able to cheat at cards by surreptitiously stealing extra cards from a deck on the far side of the table ("The Quality of Mercy").
Centauri are also known to have two hearts. One is simply a pump, much like a human heart, but the other is a complex mass of small blood vessels that functions in many ways like the human liver ("The Very Long Night of Londo Mollari").
The Centauri race produces telepaths, but how many isn’t known. There appears to be no effort to suppress telepaths or actively breed them. We have seen at least one Centauri telepath using his abilities for personal gain in a mercenary fashion ("Passing Through Gethsemane"), so Centauri telepaths apparently work without the restrictions of an organization like the Psi Corps. Emperor Turhan was known to employ four telepaths who had been raised together since childhood, creating such an intimate relationship that they could telepathically communicate with each other over interstellar distances.
The Centauri have demonstrated precognitive abilities, as well. Lady Ladira foresaw the death of Lord Kiro at the hands of the Shadows, but her vision of Babylon 5 being destroyed (a vision she was able to share with Commander Sinclair, incidentally) was averted. Lady Morella foresaw that Londo and Vir would each become Emperor in turn, and Londo had prophetic dreams of his own dealings with the Shadows and eventual death. In fact, Londo claimed that all Centauri foresee the circumstances of their own deaths in dreams ("Midnight on the Firing Line"). No other race, except perhaps the Vorlons, has shown this kind of prophetic ability.
