John Logan was a crazy racist senator from Illinois before the Civil War. His political claim to fame was helping pass a law that made it illegal for black people to settle in his state. Like a lot of northerners, his racism didn't necessarily stop him from thinking the Confederates were traitors, so when the war started he signed up to fight for the Union.
Seeing slavery up close changed him, though. Watching his army take in abused and exploited men, women and children forced him to recognize the inherent humanity in the people he had formerly despised. He reacted in horror and disgust when his men rescued a teenage girl who had been kept as a sex slave. In his letters home, he openly denounced his previous beliefs, and, unlike Sherman, his commanding officer, began to see crushing slavery and providing restitution to the former slaves as the whole point of the war; to bury slavery and treason together in the same grave. When he came home, he was the target of multiple assassination attempts, which usually ended with him taking out his attackers with whatever happened to be on hand (he used a glass pitcher twice, weirdly enough). His own family despised him; his mother refused to let him enter her home, and his sister heckled him during his campaign rallies (his wife once beat her sister in law with a wooden folding chair after she said she hoped Logan would fall in battle)
Alt-right dipshits and conservatives love to pretend the "woke agenda" is about demonizing every "hero" from this nation's past. Nothing could be further from the truth. Our nation has a great many heroes: flawed men and women who nevertheless stood up for the right thing when it was dangerous to do so. Logan is an excellent example of a man who was willing to confront his own evil beliefs and actions, and dedicate himself to change. He was a man of action, a fierce soldier, a daring general beloved by his troops, and a halfway decent politician who did a near-180 on his previous political views. He's proof that hating racism is as American as apple pie, and that anyone can change as long as they've got the balls to do it.