Catholic Encyclopedia, "he shares with the venerable Bishop Challoner the reputation of being one of the two most prominent Catholic students during the first half of the dreary eighteenth century, when the prospects of English Catholics were at their lowest."
I just spoke of the "dreary" Long Eighteenth Century, and Father Butler's work during it, on my radio program last Saturday on Radio Maria US.
More about Father Butler, from the same source:
[He was born] at Appletree, Northamptonshire, England; [and died] at St-Omer, France, 15 May, 1773. . . . After the death of his father in 1712, he was sent to the celebrated "Dame Alice's School", at Fernyhalgh, in Lancashire. From thence while still young he was transferred to the English College at Douai, where he went through the full course, and was ordained priest in 1735. He had already gained a reputation for extraordinary diligence and regularity, and was asked to remain at the college as professor, first of philosophy, later on of theology. During his years at Douai, he devoted himself to what became the great work of his life, "The Lives of the Fathers, Martyrs and Other Principal Saints". His mastery of ancient and modern languages fitted him specially for a task which involved such wide reading, while his unremitting industry and steady perseverance enabled him to overcome all obstacles. He also assisted Dr. Challoner, by preparing matter for the latter's "Memoirs of Missionary Priests", the standard work on the martyrs of the reign of Elizabeth and later. Butler's notes are still preserved at Oscott College.
Read the rest here. There are now many editions of "Butler's Lives of the Saints", updated and edited, and some might be far from his original work.