When Jason Isaacs was crafting the voice for Lucius Malfoy, he wanted something that sounded incredibly pompous, patronizing, and grating. He drew direct inspiration from an art teacher he had in drama school, who used to critique his work in a deeply condescending, whispery, aristocratic tone that drove Isaacs mad. To add an extra layer of bizarre menace, he mixed that teacher's voice with the precise, clipped cadence of a British news presenter he thoroughly disliked. When he debuted the bizarre, slithering voice on set, director Chris Columbus was initially terrified it would sound ridiculous, but J.K. Rowling herself visited the set, heard it, and declared that it was exactly how she had imagined the character sounding in her head.
