Who is Herod Sayle from Stormbreaker and what is their importance?

Herod Sayle is an Egyptian man raised in England. As a small boy Herod Sayle is one of a large family living on the edge of poverty. Sayle had been walking down the street one day and had saved an English couple from being crushed by a piano. The couple are so grateful to Sayle that they bring him to England and educate him in the English school system. There Sayle is terribly bullied by all his classmates, including the man who would one day become Prime Minister. This causes Sayle to nurse a grudge all his life. Sayle plots to donate computers to all the schools across the country and release a smallpox virus through them that will kill all the schoolchildren and leave the Prime Minister with some of the guilt.