Who is Cei from Here Lies Arthur and what is their importance?

Cei is Arthur's brother; Cei is devoted and loyal and even when provoked does not think of betraying Arthur. Cei is described as an enormous and strong man; a warrior through and through. He appears to place his warrior duty above any personal life. Cei also values the lives of his subordinates and attempts to provide for them and protect them as far as is realistic for their lifestyle. Because of this, Cei is respected as a man and a leader and his opinion carries great weight with the men.