Nikabrik

Nikabrik was a Black Dwarf and Old Narnian leader and adviser.

Narnian Revolution
Nikabrik, along with Trumpkin and Trufflehunter, found Caspian X and cared for him after his horse fled and left him stranded in the woods. Nikabrik was pessimistic in nature and reluctantly agreed to follow Caspian's leadership when the other Old Narnians chose him as their leader. Although he seemed to be consistently loyal to the Old Narnians, Nikabrik also seemed to believe that the Old Narnians should not be ruled by the likes of a human, even an honest one like Caspian.

Soon, the dwarf began to stray from Caspian and the others, showing a darker side that was hungry for rebellion. The Old Narnians assumed that Susan's horn, an emergency calling device, hadn't worked during the Second Battle of Aslan's How. Nikabrik saw by this that the Old Narnians needed a more powerful commander and, therefore, decided the only way for the Old Narnians to survive their revolution against the king Miraz, was to select a stronger leader than Caspian. Secretly, Nikabrik met with a hag and a werewolf to try and resurrect the evil White Witch, whom they celebrated as a hero and wanted as their new leader. Nikabrik, realising that Caspian was aware of his plans to overthrow him and resurrect the witch, suddenly attacked Caspian and his allies. However, Nikabrik's attempt to kill Caspian failed when the lights went out and in the mayhem, Nikabrik, instead, was killed by either Edmund or Peter Pevensie.

Traitor?
It remains a mystery to what extent Nikabrik can be considered a "traitor". He always seemed faithful to the Old Narnians, and never sided with their enemies, the Telmarine-Narnians. However, Nikabrik did try to kill the Old Narnian King Caspian X because Nikabrik saw him as an ineffective leader. It is probable that Nikabrik actually believed Caspian's death would have been best for the Old Narnians, and also probable that the assassination attempt was fueled by Nikabrik's dislike of human beings in general.