Rodolphus wanted nothing more than to please his wife, Bellatrix. He was to impress her, so she would not see him as a pathetic weak fool. Bellatrix saw Rodolphus as nothing more than that pathetic weak fool, and she used his love for her to manipulate him. Bellatrix wanted nothing more than to please her Master, the Dark Lord. She wanted to impress him, so he would not see her just as an obsessed weak woman who had lost her mind. Voldemort saw Bellatrix as nothing more than an obsessed woman who had lost her mind after Azkaban and he used her obsession for him to further his mission.