I always felt that Grant's accomplishments had been given short shrift. Only in America could a man with multiple failures in life rise to greatness.
But someone that I'd like to see reevaluated by historians is Grant's friend William Sherman. Here's a reluctant warrior, running a Louisiana military academy and accepting of slavery. But when asked to turn against his country he resigned. He then met with President Lincoln and considered him hopelessly naive about what was to come.
But when he did engage he excelled. Along the way he suffered a mental breakdown only to come back to command. When his friend Grant tasked him with conquering Atlanta and then marching North to attack Gen Lee's flank he became a legend.