Obama: Emil Jones Jr.
You don’t jump from state senator to U.S. senator as quickly as Obama did without some support. Emil Jones Jr., the president of the Illinois State Senate and an old gear in Chicago’s political machine, made Obama’s ascension his personal cause, shepherding him through the valley of political peril. The two first met while Obama was a community organizer in Chicago — in fact, Obama was protesting outside of Jones’s office, trying to secure funds for his group. Jones took Obama under his wing when he entered the State Senate in 1997, reining in jealous rivals and sending Obama important bills to raise his profile and build his credentials in anticipation of a national Senate run. Obama refers to Jones as his “political godfather,” and indeed, when Obama asked how Jones secured the endorsements of a couple fellow state senators for him, Jones replied, in godfather-esque fashion, “I made them an offer. And you don't want to know.”

Romney: The Head Bainiac
Even before graduating from Harvard Business School, Romney was being courted by the prestigious Boston Consulting Group, where he would ultimately work for a while before decamping to relative newcomer and hot shot Bain & Company, the brainchild of Bill Bain. At the company, Romney quickly rose through the ranks, getting the green light to start a sister venture-capital fund, Bain Capital, which would earn him a fortune. While perhaps not a mentor in the official tutelage sense of the word — though Romney's unofficial biographer Hugh Hewitt did use the label on Bain — Romney took to heart several of his former boss's truisms. "Bill Bain had often said there is a scientific basis for trusting your gut instincts. He reasoned that there are all kinds of signals, body language signals that your subconscious brain detects without you even being aware of it," Romney wrote in Turnaround. "Whether or not that is so, I've tended to listen to what I feel in my heart about people." Also in the book: "Bill Bain, my old boss, used to joke that most things can be fixed, but smart — or dumb — that's forever."