L. Frank Baum
The International Wizard of Oz Club publishes a thrice yearly journal, The Baum Bugle, with Oz scholarship and essays, maintains member bulletin boards, sponsors conventions, etc.
There is an extensive fan site maintained by Eric Gjovaag at The Wonderful World of Oz website.
L. Frank Baum's Wikepedia entry is quite extensive.
Piglet Press maintains a site, The Oz Encyclopedia, with much information about L. Frank Baum and his literary creation.
An extensive essay by Linda McGovern at the Literary Traveller site provides an extended biographical discussion of L. Frank Baum.