Cornelia

Cornelia is the second princess of the Britannia Imperial Family and, as such, Lelouch's half-sister. She is extremely skilled in Knightmare Frame combat and completed the establishment of Area 18 shortly before arriving in Area 11.

Cornelia is the Chief General of the Imperial Army and goes to Area 11 to apprehend Clovis's murderer, the mysterious Zero, as well as avenging Lelouch and Nunnally (unaware of the fact that they survived their predicament as political hostages) by putting an end to the conflict there. This loss of the three siblings seems to be the source of her distrust toward foreigners and Honorary Britannians. She pilots a customized Gloucester Knightmare Frame and has her own circle of devoted officers. After Clovis' death, Cornelia becomes the new Governor-General of Area 11.

As a child, she appeared to have doted upon her younger sister Euphemia; as a result, Euphemia is Cornelia's only known weak spot. Clovis believes that she and Prince Schneizel know about the truth regarding the murder of Marianne Vi Britannia, although Euphemia later tells Lelouch that Cornelia has long idolized Marianne and conducted investigations on the murder.

Gilbert

Confidante and personal knight to the Second Princess Cornelia, who arrived in Area 11 as a member of the princess' contingent; a slender, dark-haired, bespectacled man. Guilford informs Jeremiah Gottwald of his demotion shortly after arrival.

In R2 Guilford's is enlarged. After Governor-General Carares is killed in the Babel Tower incident in season two, Guilford serves as a temporary Governor-General to Area 11. At one point he uses the Black Knight's POWs to goad Zero into a duel, but is defeated when Zero uses ground mechanics underneath the dueling area. He later joins up with Lloyd and Cecil and uses a Blue version of the Vincent Knightmare along side the Knights of Round.

(Taken from Wikipedia)