The White Demon (دیو سپید, Div-e Sepid) is what the whole journey was for, and he is the seventh stage. He is at the bottom of a cave, and the poem takes care to say that the dark down there is not ordinary dark.

He is the strongest thing in the Shahnameh that is not a person, and what makes the episode famous is not how big he is. It is that Rostam reaches him last, after six stages that have each taken something out of him, and has to do it anyway.

What he did to the people who came before, and what is needed from him afterwards, is the hinge the whole Mazandaran story turns on. That part belongs to the poem, and to the seventh khan.