You can also find biographies of particular mathematicians by doing keyword searches on their names in SOUTHcat, the University Libraries' catalog at http://southcat2.usouthal.edu/vwebv/searchBasic
Searching Google or another search engine using a particular mathematician's name, for example: Hypatia, Euler or Ramanujan, will help you find web sites with biographical information specific to that person. Here are some general biographical web sites for mathematicians.