In the 2008 campaign, Obama presented himself as a kind of 21st century Abraham Lincoln. Launching his candidacy outside the Old State Capitol in Springfield, Illinois, where Lincoln had made his "House divided" speech, Obama referred self-consciously to the “tall, gangly, self-made lawyer” in whose steps he followed. When it came time to appoint a cabinet, he was photographed carrying a copy of Doris Kearn Goodwin's Team of Rivals, which tells the story of how Lincoln appointed to his cabinet his three main competitors for the presidency in the 1860 election, despite their open enmity towards him, because he thought it was the only way to hold the Union together during the Civil War. During the 2008 transition period, Obama let it be known he was of the same mind, telling Time magazine, “I don’t want to have people who just agree with me. I want people who are continually pushing me out of my comfort zone.” The biggest manifestation of this approach was, of course, his appointment of Hillary Clinton to State.
Vanity Fair's Todd Purdum argues that the reality of Obama's cabinet has been rather different, and that with the important exceptions of Hillary Clinton, Tim Geithner, Robert Gates and Leon Panetta, Obama has surrounded himself with a cabinet of loyalists and non-entities. I'm not sure this is fair, particularly once you get beyond the cabinet itself. If you add the first chief of staff, Rahm Emanuel (not a shrinking violet), Joe Biden, who has been allowed to play an influential, free-ranging role in the administration, and Larry Summers - not in the cabinet but in a powerful position and hardly a quiescent figure - then that's a pretty long list of exceptions. On two of the toughest decisions of a presidency that has been filled with them - the early economic crisis, and Afghanistan withdrawal - Obama allowed and encouraged a genuine internal debate (indeed, you might argue that on these issues and healthcare, he didn't exert his own point of view early and forcefully enough).
There is some truth in the suggestion that Obama doesn't particularly like being outside of his comfort zone, however, despite his protestation. Every insider account of his administration has made the point that he doesn't often seek out views beyond his inner circle of advisers (most of them from the campaign) and that he is unusually self-contained (a former adviser tells Purdum, “He’s a total introvert. He doesn’t need people.”) When he appointed an independent-minded outsider, Bill Daley, to be his second chief of staff, the result was disastrous, and Daley was replaced by a 2008 veteran. So although Obama can handle big personalities being in the room, he retreats to his loyal core, or simply to himself, when it comes to decision-time.
To return to Hillary - well, to her credit, she turned out not to be interested in being a rival at all, but merely in doing a good job as Secretary of State, which, although good for the country, won't make very juicy material for a future historian.