The standard popular history recommendation is Edmund Morris's trilogy. I would argue that the trilogy brilliantly captures the essence of TR while being less effective when forced to delve into the nitty-gritty of the political world (especially in Theodore Rex). Morris also makes historians uncomfortable by stretching some of his sources to a breaking point when he tries to paint a picture of a scene or delve into the minds of some of the major personalities in the books. Morris comes across as less of a historian and more of a writer.

That being said, The Rise of Theodore Roosevelt is superb, and Morris did shine a light on other aspects of Roosevelt that had been underplayed (such as the Venezuelan Crisis of 1902-03, which he looked at in Theodore Rex).