It is interesting. I was reading a c-span interview with Romney from 2006, and he explained that he was known as "Billy" until age 5, when he got upset at the lyrics of a song . So his mother suggested he use his middle name, and it's been that way ever since.  The interview was conducted by Brian Lamb, who (shameless plug!) interviewed me for the same program last week.  This is from the Romney interview:  BRIAN LAMB, HOST: Willard Mitt Romney, where did you get those first two names?  GOV. MITT ROMNEY (R), MASSACHUSETTS: A little unusual. Willard was after J. Willard Marriott, the founder of the Marriott Hotel chain. He was my dad’s very close friend. They were both boys in Utah, moved back here to Washington, D.C., so I was named Willard after J. Willard Marriott.  Mitt is my given middle name, and that’s after a man named Mitt Romney who in the 1920s was a professional football player for the Chicago Bears, quarterback, and the greatest athlete the Romney family has ever known. So I’m really named after two great heroes, one an industrialist and the other a great athlete.  LAMB: Why did you pick Mitt over Willard?  ROMNEY: Well, I actually used the name Billy when I was in kindergarten. And there was a song when I was a boy called ”Oh Where Have You Been, Billy Boy, Billy Boy? Oh Where Have You Been, Charming Billy?” And it talked about kissing and your mother and so forth. And I decided that was a terrible song. And I came home and said, I can’t live with that name any longer.  And I talked with my mom about what name I could use. She said, well, you could use your middle name. And so sometime in kindergarten I switched to Mitt and I have been on the Mitt name ever since.
The Post's fact checker, Glenn Kessler, chatted about who told facts who spouted fiction during Thursday's South Carolina Republican candidate debate.