A Klingon ambassador who secretly worked with the Romulans to break the Federation-Klingon alliance using a brainwashed Geordi La Forge.
Kell is a Klingon ambassador sent to deal with a rebellion on the Klingon colony of Krios, whose governor Vagh accuses the Federation of arming the rebels. Behind his diplomatic manner he is a traitor collaborating with the Romulans.
In The Mind's Eye, Kell uses the signals of La Forge's conditioned VISOR to control him, steering him to smuggle weapons and finally to attempt to kill Vagh. Data exposes the scheme, and Kell is handed over to the governor. Kell then asks Picard for asylum, which Picard refuses.