Arthur

Arthur (アーサー, Āsā) is a friendly feline who was originally found by Euphemia and was befriended, before joining the Student Council members. It is always biting Suzaku and is usually with him or Anya Alstreim.

First Season
It is a stray cat which Third Princess Euphemia befriends after she arrives in Area 11. Arthur is later chased throughout the school grounds by the entire student body after wandering into the Lamperouge residence and escaping with Lelouch's Zero mask. Milly announced that the one who would catch the cat would get a kiss from any member of the Student Council. Suzaku and Lelouch were the ones that got the cat and got a kiss on the cheek from Nunnally. The student council adopts it and builds a cat house in the council room. A running gag in the series involves Arthur constantly taking a bite at Suzaku's hand or leg. Despite this typically one-sided relationship, Suzaku takes the feline along with him to Britannia.

Second Season
When Suzaku returns to Ashford Academy in the second season, he brings Arthur back with him. During his time home, Arthur takes a liking to Knights of the Round member Anya Alstreim. In the Avalon, it was sitting in front of Lelouch and acted like it knows what was being said and agreeing on what Lelouch said. In the series finale, Arthur is shown watching over Suzaku's grave in the middle of the night. Arthur is last seen in Ohgi and Viletta's wedding picture on Anya's head, suggesting that she's his new owner.

Audio Drama
In the Code Geass Audio Drama series, Arthur was featured in one of the episodes (episode 6.113 - The Name of a King) where the members of the Student Council had just adopted Arthur and were trying to decide a name for it, but earlier Euphemia had already given the cat the name 'Arthur'.

Some names suggested for Arthur included:
 * Panda (for the black spot around its right eye)
 * Schrodinger
 * Tama
 * J. C. Maxwell
 * Doppler
 * Michelle

The student council decided they were going to name the cat 'Lelouch the Second' and were actually going to go through with that name until Nunnally came in and started talking to the cat. After she announced that the cat's name was Arthur, everyone agrees to it and Suzaku muses how Nunnally and Euphemia gave the cat the same name.

Trivia

 * In popular medieval history, Arthur is the name of the king who established the seemingly similar "Knights of the Round Table" as opposed to the "Knights of the Round" of the series.
 * it could also be that the name refers to the british science fiction Arthur C. Clarke known for his work "2001: a space odyssey"
 * Arthur is voiced by Michelle Ruff who also does Euphemia li Britannia, Lelouch vi Britannia (child) and Mutsuke Minase. She also voices Rukia Kuchiki in Bleach.