Born in Ireland in the mid-nineteenth century, Agnes Mary Clerke achieved fame as the author of A History of Astronomy during the nineteenth century. Through her quarter-century career, she became the leading commentator on astronomy and astrophysics in the English-speaking world. This biography describes not only the life and work of this extraordinary woman, but also chronicles the development of astronomy in the last decades of pre-Einstein science. Along the way, it introduces many of the great figures in astronomy of that age, including Huggins, Lockyer, Holden, and Pickering.