Use these databases to locate general information about people that encountered a specific event and/or a specific person.
Oliver Wendell Holmes Library Catalog
Google can also be very useful for biographical information. However, it is important to Google WISELY. Remember the ABCs of website evaluation: authority, bias, and currency. If you are not sure if a website is legitimate or cite-able, just ask a librarian!
Did your person create or found an organization? Perhaps that organization has a page dedicated to that person and their history.
Museums can also be great places to go, even if your focus is not on art or an artist. Consider the following: