Riis is considered one of the first representatives of undercover investigative journalism. For example, he worked in a meat factory under a different name. Riis' fame is based on his book publications How the Other Half Lives, a powerful documentation of life in the New York slums. His works helped improve housing conditions in New York tenements, as well as school reforms. In connection with his social documentary reportages, he developed a friendly relationship with Theodore Roosevelt, who was New York's police commissioner back in 1895.