If you want to know about someone's life and work, libraries provide a rich array of sources. To help you locate them, tools such as Biography Index and the Biographical and Genealogical Master Index are generally available.
Directories that list the basic information regarding prominent people - degrees, work history, honors, address, etc. - include Who's Who in the United States, Who's Who in Politics and American Men and Women of Science. For more detailed biographical sketches, you may want to consult Contemporary Biography, Contemporary Authors, or Politics in America.
Several biographical sources contain substantial entries of people who have died: prominent Americans are covered in The Dictionary of American Biography, British figures in The Dictionary of National Biography. Prominent scientists from every nation and period of history will be found in The Dictionary of Scientific Biography.