To find books ABOUT people, consider each of the following tips:
Look in dictionaries and encyclopedias. Search both Quest and MOBIUS using these LC subject headings to find more: Mathematicians - dictionaries and/or Mathematicians - encyclopedias
If the person is contemporary, they may have an obituary.
Be aware of more than one name, for example: Euclid as well as Euclides.
Check bibliographies in books, articles, and even dictionary or encyclopedia entries, including the Wikipedia bibliographies!
There may be biographical information in a book the person has written. Find something they've published and read the preface or front pages.
Check more than one source! Different information can be found in differnt sources. Weave the tidbits of information you find in several sources to create your own report.