Marcia Anastasia Christoforides (born July 27, 1910 - died October 28, 1994) was a philanthropist, an art collector, and noted owner of racehorses.

Born in Sutton, Surrey, England, she was the daughter of John Christoforides. A very bright young lady, for a number of years she worked as personal secretary for the wealthy Canadian financier James Hamet Dunn, 1st Baronet Dunn. Eventually their working relationship became personal and although thirty-six years her senior, in 1942 she became his third wife. Intensely loyal, she had been a devoted employee and he would seek her input on most every business matter for the rest of his life. The couple maintained homes in England, France, and at the Canadian seaside resort of St. Andrews in New Brunswick, the province of her husband's birth. In the late 1940s, Lady Dunn and her husband developed a friendship with the Spanish artist Salvador Dali who painted several portraits of them. These works are now on permanent display at the Beaverbrook Art Gallery in Fredericton, New Brunswick.

Known as Christofor to her family and friends, on the passing of her husband in 1956 she was the beneficiary of a large estate and became the administrator of a fund to be used for charitable purposes. One of her late husband's closest friends was his fellow New Brunswicker, Max Aitken, 1st Baron Beaverbrook who acted as her advisor. The two developed a very close friendship and Lord Beaverbrook, who had been a widower for many years, came to have great admiration for her and her abilities. In June of 1963 the eighty-four-year-old Beaverbrook and the fifty-three-year-old Marcia Anastasia Christoforides-Dunn were married. Lord Beaverbrook had already used his fortune to greatly benefit the citizens of the province of New Brunswick in Canada. By virture of their marriage, Aitken was able to name her the legal overseer of a large part of his estate that he wanted to go to more charitable works.

Lord Beaverbrook passed away one year after their marriage and Lady Beaverbrook was left in charge of a large benevolent fund. With that, and the funds from her first husband's estate, she became one of Canada's most prominent and selfless philanthropists. On behalf of her first husband considerable funds were donated to his alma mater, Dalhousie University in Halifax, Nova Scotia. In 1967, she was awarded an honorary Doctor of Law (LL.D.) from that institution and in 1968 she was appointed the University's Chancellor, a position she held for the next twenty-seven years.

A devotee of show horses and equestrian events, she was also a leading race-horse owner. Amongst the many thoroughbreds she owned were:

• Niniski - a son of the great Nijinsky II, he won the 1979 Prix Royal Oak at Longchamp in Paris, France and the Irish St. Leger Stakes then became one of the leading sires on the flat turf.
• Minster Son - won the Town Moor classic and the St. Leger Stakes in 1988
• Mystiko - won the 1991 Two Thousand Guineas
• Petoski - won the 1985 Prince of Wales's Stakes and the King George VI & Queen Elizabeth Diamond Stakes
• Endoli - won the Aston Park Stakes at Newbury
• Bustino - won the 1974 St. Leger Stakes

Although the most altruistic of people, Lady Beaverbrook's high-profile in British society and the publicity from her philanthropic work resulted in a near tragedy. On May 4, 1971 a bomb was strapped to the underside of her automobile, placed there by The Angry Brigade, a British terrorist group. Fortunately it was found in time.

Lady Beaverbrook passed away in 1994 having given away the equivalent of nearly $300 million (at today's value) to support education, cultural undertakings and wildlife preservation. In addition to the charitable trusts from both of her husbands, the Christofor Foundation for charitable purposes was established by friends out of her personal estate. A lover of animals, among the many philanthropic causes Lady Beaverbrook supported, the Christofor Foundation established the Sir James Dunn Animal Welfare Centre at the University of Prince Edward Island with a $2.2 million gift. Amongst other worthwhile causes, the Foundation from her personal estate also helped fund the Science East Association in Fredericton, New Brunswick. Because the Province of New Brunswick was home to both of her husbands, it contains many institutions built with funding from their estates. However, large contributions were made to numerous causes throughout the four Atlantic Provinces, most notably in education. In her memory, the Sir James Dunn Foundation of Saint John, New Brunswick made a $1 million donation toward the establishment of Christofor Hall at Acadia University in Wolfville, Nova Scotia.

Marcia Anastasia Christoforides' story was told by Australian author and historian Ann Moyal in her 1995 book .