Stevens was from Pennsylvania, so I read this for a historical article I wrote for the newspaper. He was a towering figure of the anti-slavery movement in the Civil War, and after Lincoln was assassinated, the became the ringleader of the fights against Andrew Johnson and of the eventual impeachment action, even though his health was rapidly declining. I recall this being a solid biography, not scintillating but interesting.
Thaddeus Stevens was to the US House of Representatives what Charles Sumner was to the Senate. The leader of the Radical Republicans in their quest for abolition, reconstruction and civil and voting rights for freedmen. I found a 1st edition of this book from 1955 and it's still a good read. The author is very sympathetic to his subject.