You can find book-length biographies, as well as chapters included in biography collections, by using the UD Catalog and searching by Subject.
Type in the person's last name, first name for best results.
These databases are good sources for articles and other biographical information on individuals.
ipl2 - Reference - Biographies
Searchable, annotated subject directory of Internet resources selected and evaluated by librarians.
White House.gov - The Presidents
Short biographies of all U.S. presidents and first ladies.