In an essay called "Grant and Lee: A Study in Contrasts" from The American Story, a series of essays by historians, Civil War expert Bruce Catton compared and contrasted Grant and Lee.
While he argues that the two men were largely dissimilar and represented different "elements" in the American experience, Catton states they shared the following traits:
Both were stubborn and faithful. They dug in and didn't give up easily. Both were tenacious fighters.
Each was a resourceful risk taker. Lee illustrated this in the "dazzling campaigns" of Second Manassas and Chancellorville; Grant at Vicksburg.
Each man rose to greatness in his ability to turn to peace at the war's end. Both Lee and Grant, Catton contends, behaved with enormous graciousness when they met briefly in Appomattox to finalize the South's surrender that led to peace.
Each man came from a different background. Lee's was backward-looking, aristocratic, and agrarian, while Grant represented the forward-looking perspective of the industrial North, but both were men of courage and conviction.