Lives of the Saints by Alban Butler

Alban Butler was a Catholic priest in the 18th century who's still remembered today for his biographies of the Catholic Church's greatest figures. Decades of work went into his seminal work, The Lives of the Saints, commonly referred to as Butler's Lives. Hundreds of years later, it is still the most comprehensive collection of biographies of saints, and it is a must read for anyone interested in Christianity and the religion's history.