Fritz Pfeffer is a real name of Mr. Dussel. He hides with the families of the Franks and Van Daans in the secret annex. He works as a dentist, and he is a friend of the Franks. Anne does not feel positive emotions to this man because she notices his bad habits. Mr. Dussel shares the room with Anne, and she has to listen to his boring lectures and see his weird habits related to hygiene. Mr. Dussel wife is a Christian, and she has decided not to hide. That is why the man is worried about her.
Mr. Dussel in the Essays