This biography of him was pretty dang good. Super fascinating.
This is a repost, but one worth reposting.
I saw this years ago and bought the book, "Be Free Or Die" to learn more about him. Highly recommend.
Be Free or Die: Story of Robert Smalls
This man should be known.
I really like reading about Robert Smalls, a slave who worked on a steamboat, stole it, made it to the Union side, rallied congress, fought for the North in the remainder of the war, and then became a congressman himself afterward.
Be Free or Die: The Amazing Story of Roberts Smalls' Escape from Slavery to Union Hero, by Cate Lineberry
There are several books about him, that's the most "history book" nonfiction style. There are others that offer a more dramatic perspective if you think your friend would prefer that instead.