This book is a fairly accademic affair, but gives a pretty good picture of the man. There's a twist in that last line as there are thought to be no surviving pictures of him, but the author thinks she may have found one.
As with other similar books there is a large section of notes, but I find it annoying to have to keep flicking to the back to read the details of some quote or remark and tend to give up after a while, even though there may be interesting material there. There has to be a better way to present that information.
I did actually finish this just after System of the World, but that's because I took this when travelling as it's a much lighter book to carry around.
My next read is about the cracking of Japanese codes during WWII. Expect a report here eventually.