Tellico Lunngrevink Letorte, alias Penstock, but to his friends, Dudu is a doppler who appears in the short story "Wieczny ogień" ("The Eternal Fire") in The Sword of Destiny.

In "The Eternal Fire", Dudu ultimately faces Geralt by taking on the witcher's own shape. This gives Geralt a very good idea of what fighting himself would be like and it is not at all certain at the outset if the "true witcher" will prevail. It all comes down to a question of conscience.