Howard Phillips Lovecraft (1890-1937) was a very productive author, who sometimes used real people, places, and events in his stories, and sometimes completely fictive people, places, and events; but who always managed to describe it so skilfully that the reader (who he didn't have very many of during his lifetime, unfortunately) never quite knew what was real and what was fiction.
Lovecraft is best known for his creation the Necronomicon, a book supposedly written by the "mad Arab" Abdul Alhazred (a name which probably originated in all-has-read, a name Lovecraft came up with at an early age as a joke for his immense interest in reading), but hardcore fans of his macabre yet beautiful stories also know about people and places such as Charles Dexter Ward, Miscatonic University, The Old Ones, Dunwich, Cthulhu, and so on. Anthony Pearsall, a devoted fan since an early age, has now created what more or less should be known as the ultimate Lovecraft lexicon, where numerous locations, people, and large as well as small influences or happenings connected to Lovecraft are described with the utmost precision.
But beware; it's a lexicon, not a traditional book in the normal sense of the word. Reading it all in one go is not recommended, and you won't have much use for it unless you're a Lovecraft fan. But to every fan - myself included - who cannot resist his stories, the book is quite frankly a must. In the beginning Pearsall offers a short yet informative biography of his hero, and then the lexicon begins... Pearsall has been EXTREMELY precise with his work, and since Lovecraft from time to time can be a very difficult author to read the book will prove very useful, for instance since Lovecraft had a tendency to use the same people, places, and events in different stories. Not only that, he was also a devoted writer of letters and reader of books, and information about these interests of his are also found in the lexicon.
So I can only recommend that you go get this book. In case you want to learn more about Lovecraft the human being, than there are other and much better books available, but to anyone interested in his literary creations, The Lovecraft Lexicon is nothing but a total must.