约翰·克里斯托夫，Christopher Samuel Youd aka John Christoher aka Samuel Youd is a British writer of science fiction who is best known for his post-apocalyptic novels 'The Death of Grass' aka 'No Blade of Grass' (1957) and 'The Gaurdians' (1970), and the popular trilogy 'The Tripods' (1967-68).