Since Alexander Thayer (a Harvard alum) published his three volume biography of Beethoven over a period of twenty-one years from 1866 -87 it has been the bedrock of information about Beethoven's life and work. It has also become a model for other musicologists and biographers. Obviously, more came to light over the next hundred years and the work was edited and reworked by Elliot Forbes (another Harvard alum and professor of music (but from a time before a Ph.D. was required)).
Forbes' "Thayer's Life of Beethoven" was published in 1964 in two volumes. (Does the name Ruth's Chris Steakhouse come to mind?) Prof. Forbes died in January of 2006 at 88 years of age. For awhile the two volumes were combined, but they are now separated. You simply must have them both. This first volume covers Beethoven's origins through 1814. The second volume from 1815 through his death in 1827 with several appendices that cover his estate, speculations about his various illnesses, lists of his works, publications of his works immediately following his death, preparations for a first biography, and so forth.
The book is organized chronologically and provides a well-documented presentation of Beethoven's activities that year whether performing, composing, or personal. It provides some speculation about certain events, but always identifies it as such. At the end of each chapter it lists the works composed that year and the works published that year.
Very much worth having. Just remember that you have to buy BOTH Part I and Part II to get the whole biography.