Che Guevara: A Revolutionary Life by Jon Lee Anderson
It only took me about 6 months to read - I would sit and read it for 3 hours then not touch it for another few weeks because I knew I'd find it hard to put it back down if I started reading again.
Great read, the author was given greater access by Guevara's family and by the Cuban government than anyone who has wrote a book on Guevara before, so it's very accurate and doesn't just focus on the political and revolutionary figure, it looks at his whole life and the sort of person he was, and gives a fairly detailed context of what was going on in world politics aside from Guevara's involvement too. I recommend it to anyone interested in him.