Rolo vi Britannia is a character that only appears in Nightmare of Nunnally who serves as one of the main antagonists in the series.
Lelouch's twin brother, who had apparently been taken from Marianne when he was a baby, due to the superstition of twin princes bringing misfortune. Therefore, his existence was unknown to Lelouch and Nunnally. He is involved with the Geass Order and known as The Cardinal. He plans to kill Nunnally and Lelouch so that he can take their powers to become the true "Demon King" and overthrow the Emperor.
He is involved with the Geass Order and known as "The Cardinal". He first appeared in chapter ten with Schneizel, who is heading to Area 11, and later meets Suzaku, who can tell that he's not Lelouch. It is revealed that he was in fact not Lelouch's twin, having been created artificially from Charles and Marianne's DNA, and was genetically unstable, like the rest of the Irregulars, ultimately resulting in his death.
His Wired Geass is known as "The Ice," with the power to "freeze time," similar to his anime counterpart. Also like his anime counterpart, it only works in a certain range, referred to in the manga as an "Absolute Territory."
Rolo has access to wired Geass powers, and is able to summon his own personal Vincent Knightmare Frame. His piloting skills are somewhat ruthless and cold.