Letter (alphabet)

There were twenty-six letters in the English language alphabet: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y and Z. (TV: The Masque of Mandragora, Midnight, Goodbye, Sarah Jane Smith, Shada, AUDIO: Shada, A Death in the Family, PROSE:, etc.)

Deciding to change their tribal name so that it was dissimilar to that of the Thals, the Dals named themselves after the first letter of their joint alphabet; Kaled. The Thals realised that by doing this the Dals were trying to less-than-subtly assert their primacy. Later, during the war on Skaro, Kaled scientist Davros came to name the mutated Kaleds he created as "Dalek" after the last letter of the alphabet as a claim of completion for his creations. (PROSE: The History of the Daleks)

Behind the scenes
Although in the real world, the alphabet goes "A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z", when Elisabeth Sladen's Sarah Jane Smith recited the alphabet backwards in she ordered U after V.