Ulysses S. Grant who won the Civil War without which Confederate states would have continued slavery for who knows how long.

Yes, he owned one slave for not quite a year, before he gave him his freedom in 1859. He also married into a slave-holding family, but his views changed. https://twitter.com/jrivanob/status/1274194145838428160

As president he was an advocate and defender for the freedman's newly acquired rights. Frederick Douglas wrote of him, “To Grant more than any other man the Negro owes his enfranchisement.”

In his memoirs, Grant wrote, "As time passes, people, even of the South, will begin to wonder how it was possible that their ancestors ever fought for or justified institutions which acknowledged the right of property in man.”