Samuel Liddell (or Liddel) MacGregor Mathers, born Samuel Liddell Mathers, was a British occultist. He is primarily known as one of the founders of the Hermetic Order of the Golden Dawn, a ceremonial magic order of which offshoots still exist today.

Mathers was born in January 1854 in Hackney, London, England. His father, William M. Mathers, died while he was still a boy. His mother, whose maiden name was Collins, died in 1885. He attended Bedford School, subsequently working in Bournemouth, Dorset, as a clerk, before moving to London following the death of his mother. His wife was Moina Mathers, sister of the philosopher Henri Bergson.

Mathers added the "MacGregor" surname as a claim to Highland Scottish heritage, although there is little evidence of such in his family background. He was a practicing vegetarian, or (according to some accounts) vegan, an outspoken anti-vivisectionist, and a non-smoker. It is known that his main interests were magic and the theory of war, his first book being a translation of a French military manual. He became more and more of an eccentric towards his later years, as was noted by W. B. Yeats.

Mathers was a polyglot; among the languages he had studied were English, French, Latin, Greek, Hebrew, Gaelic and Coptic, though he had a greater command of some languages than of others. His translations of such books as The Book of Abramelin (14thC.), Christian Knorr von Rosenroth's The Kabbalah Unveiled (1684), Key of Solomon (anonymous 14thC.), The Lesser Key of Solomon (anonymous 17thC.), and the Grimoire of Armadel (17thC.), while probably justly criticized with respect to quality, were responsible for making what had been obscure and inaccessible material widely available to the non-academic English speaking world. They have had considerable influence on the development of occult and esoteric thought since their publication, as has his consolidation of the Enochian magical system of John Dee and Edward Kelley.

Mathers died in November 1918 aged 64.