Who is Ulysses S. Grant from The Last Full Measure and what is their importance?

President Lincoln promoted Grant to lead the entire Federal army after he displayed strong leadership skills in battle. Grant, in turn, brought a stubborn determination to the war that hadn't been there before. Unlike Lee, he often expressed his anger in terms that were unmistakable. He took responsibilty for his mistakes, but he was always certain that winning the war was only a matter of time.