Unoffical Members of the Round Table

The Unoffical Members of the Round Table consists of the three most important moral compasses of the Knights of the Round Table: Queen Guinevere; the wife of King Arthur of Camelot and the sister of Sir Elyan, Merlin; King Arthur's most trusted servant and best friend and Gaius; Camelot's Court Physician. Though not official members of the table, the trio sit in on the meetings of the Round Table and allow their opinions to be heard by the knights and Arthur and occasionally join them on quests.

Trivia

 * According to promo trailers currently launched for Series 5, it is seen that Merlin is standing up away from the Round Table during one particular meeting, yet there is an empty seat between Gwen and Elyan. This seat was confirmed in the opening episode of Series 5 to be Gwaine's seat. He had been kidnapped along with Percival and several other knights six weeks prior to the beginning of the episode which would explain why there was an empty seat at the table.
 * According to the promo trailers, Gaius is seen sitting on one side of Arthur while Gwen is seen sitting on the other. Whether this means that they offical members of the court as the Queen and the Court Physician respectively or because they are two of the most important members of Arthur's inner circle is unknown as of yet.
 * It was seen in Arthur's Bane: Part Two and The Death Song of Uther Pendragon that Mordred is an offical member of the Round Table as Arthur knights him after saving his life at the end of Arthur's Bane: Part Two putting any speculation to rest about his status at the Round Table and as a Knight.