With The Wonderful Wizard of Oz being a popular piece of Americana, of course people have wanted to know more about the life of the man who created it. Jack Snow, to my knowledge, was the first to attempt a Baum biography, though he was unable to complete it. In the back of Who's Who in Oz, he did include a biographical sketch of Baum and the other writers and illustrators of the (then) thirty-nine Oz books. The printed version has Baum's biography span four pages: the longest of the biographies. In its brevity, it shows a few inaccuracies, but that was due to the limited information available at the time.
The first book-length Baum biography was To Please A Child, published in 1961 by Reilly & Lee as part of their attempt to relaunch the Oz series. (This joined picture book versions of the first four Oz books, The Visitors from Oz picture books, and soon Merry-Go-Round in Oz and the White Edition Oz books.) The book was by Frank Joslyn Baum and Russell P. MacFall. However, Frank J. Baum had died during the writing process, leaving MacFall to try to tie what was left together. This led to many inaccuracies in the text and even a few cases of MacFall inventing situations out of whole cloth, including a brief mention of Baum leading a march in support of William Jennings Bryant. I have heard, though I'm unsure of the veracity of the claim, that Frank J. Baum actually didn't have a lot of research resources at hand.
Having heard about the inaccuracies, I had avoided getting To Please A Child for a long time, but when an Oz collector recently offered a nice copy for sale, I decided to go ahead and get it. The book contains many Baum family stories that may or may not be true (in the manner of Baum himself, sometimes the truth isn't such a great story), including the "Affair of the Bismarcks" and the famous origin of the word "Oz" from the filing cabinet. The book is also known for misportraying Maud Baum as a tyrannical mother and wife.
To me, one of the bigger issues was how MacFall offers a chronological life of Baum up until The Wonderful Wizard of Oz was released, then dedicates chapters to the success of the book and the series, breaking the chronological account of Baum's life. The remainder of Baum's life is retold rather simply in a few more chapters. It did, however, offer a few good bits of information: apparently not even ten years after Maud Baum's death, Ozcot was already torn down and an apartment building on its site.
Fortunately, by this time the International Wizard of Oz Club had been formed and was well underway with research of Baum's life and the creation of the Oz series, often finding where To Please A Child had dropped the ball. There have been many Baum biographies over the years, but I shall focus on the three that I've used for reference the most.
One cannot talk about Baum biographies without mentioning Michael Patrick Hearn. While he has yet to publish his critical biography of Baum (I have heard it is finished, they are simply awaiting a good time to release it, though Hearn probably is yet putting finishing touches on it), he did include a nice biography of Baum in his groundbreaking work The Annotated Wizard of Oz. While far from the first serious study of the Oz books, this book offered a reprint of The Wonderful Wizard of Oz with annotations in which Hearn speculates on how the story is being told in the context of Baum's life and the larger work of the Oz series and the literary world. Thus, this put Oz in the eye of critically examined literature. The book was first published in 1973, but was heavily revised and expanded in 2000. (The shape of the book changed in 2000, so it was less like the original edition of The Wonderful Wizard of Oz.) The lengthy introduction by Hearn offers a lot of good information about Baum's life as well as numerous photos. The appendix includes a bibliography of Baum's works.
Hearn's research was later used as the basis of the 1991 television film The Dreamer of Oz, though, in Baum tradition, that film took many opportunities to make the truth sound like a better story.
Mother and daughter pair Jean Shirley and Angelica Shirley Carpenter (now a former Oz Club president and a friend) produced L. Frank Baum: Royal Historian of Oz in 1992. While aimed at young readers, this biography was actually very well-done and researched and featured numerous pictures, definitely benefiting from the research that had been published in The Baum Bugle.
Finally is Katherine M. Rogers' L. Frank Baum: The Creator of Oz, published in 2002. A more studious biography of Baum's life, it is able to put his life and works into a good historical perspective with quite a bit more research.
While not Baum biographies, I should make mention of two books edited by Nancy Tystad Koupal: Our Landlady and Baum's Road to Oz, both of which focus on Baum's years in Aberdeen, South Dakota.
The less studious might ask, "Why get multiple biographies of someone? Shouldn't one good one be enough?" Perhaps, if one just wishes to know about the person's life, but to my knowledge, there is not a biography of a person that has been declared "definitive," in that that one book contains all the information you'd need to know about a person's life. Although I do look forward to the day Michael Patrick Hearn releases his critical Baum biography, I doubt that book will be the be all and end all source of information about Baum. Multiple sources of information are always best on a topic.