"A couple of months went by and I totally forgot about it," Hill says. "I came home one day, a particularly beaten-down day, opened up the mailbox and there's this letter from David. He was moving to Washington to work on the Truman book. ... I called him the next day, and he said he had research assistants before but they hadn't worked out too well. 'Since you're here and I'm here, let's have lunch.'"
Word spread about his good work. McCullough introduced Hill to a young documentary maker named Ken Burns, then in the middle of a film about the late Louisiana populist Huey Long and soon to begin his Civil War documentary. He jokes about having to share Hill's time with McCullough.
"You could tell it was a dutiful decision on David's part whether he would let me know about this extraordinarily resourceful human being," Burns explains with a laugh. "He [McCullough] just said, 'If you need a blue Volkswagen turned upside down on a downtown street tomorrow morning, he'll figure out a way to do it.'"
Historians praise Hill not just for the obvious gifts of knowledge and agility, but as one who pushes just a little harder than other researchers and gets archivists to do the same for him. Jeffrey Flannery, who heads Reference and Reading Services for the Library of Congress' manuscript division, has known Hill for years.
"Any archivist gets some deep satisfaction to see the collections used," Flannery says. "And Mike is a vital cog in that. You help him as he does his work and a couple of years later there's a book using our materials."
A resident of Frederickburg, Va., Hill spent a recent afternoon at the manuscript division, looking through a bound Washburne journal that was perched on a foam rubber easel. But he also has traveled with McCullough from Paris and Maine to the Truman library in Independence, Mo. He visited England to help Michael Korda research a biography of T.E. Lawrence. Philbrick was glad to have Hill along for "The Last Stand," about the Battle of the Little Big Horn.
"I wanted to retrace Custer's steps, 300 miles over sparsely populated terrain," Philbrick says. "We were out there on the terrain and got stuck in the mud in the place where Sitting Bull was killed. We've had all sorts of adventures and having him there was an immense help."
Like a beloved supporting actor, Hill need only worry about keeping up with his commitments. McCullough has him lined up for a second book on Americans in Paris, this time moving ahead to the 20th century and the impact of air travel. He's helping Philbrick on a Revolutionary War book, Korda on a biography of Robert E. Lee and former Mondale chief of staff Richard Moe on a study of Franklin Roosevelt. Hill is even attempting another book of his own, about World War I poet Alan Seeger, best known for "I Have a Rendezvous With Death."
"I'm drawn to his story," he says of Seeger, the uncle of musician Pete Seeger. "There have been some small, but not particularly good bios of him long ago. There is new archival material on him. And the centennial of World War I is coming up in a few years.
Hill adds: "It will take me a long time to do it."