Who is William from Reconstruction: America's Unfinished Revolution, 1863-1877 and what is their importance?

William "Boss" Tweed was a politician in New York City who defrauded the city of millions of dollars. Some of that maoney was used to help immigrant families. Tweed controlled both the appointment and elections of city officials. His career ended when he was prosecuted by Samuel Tilden, who later ran for president.