J

As spoken by the Tenth Doctor and the entity possessing Sky Silvestry, J was the tenth letter of the alphabet, following I and preceding K. (TV: Midnight)

It was "the forbidden letter" of the Dalek language: added to the beginning of any sentence or phrase, it added an insulting meaning to it. For example, whereas "galkor" simply meant "Follow me, I am your guide", "j'galkor" would come across as "Follow me, weaking! I am your guide". (PROSE: The Dalek Dictionary)

In 2050, mother and daughter June and Jorjie Turner wore matching gold necklaces in the shape of the letter "J". (TV: Regeneration et al.)