Mary Hayward Weir, born Mary Emma Hayward (1915–1968), was an American steel heiress and socialite. She was the wealthy widow of Pittsburgh steel king Ernest T. Weir, and the former wife of author Jerzy Kosinski.
Born in Indianapolis, Indiana, she was working as a secretary for the National Steel Corporation in 1938 when she met and later married her boss, Chairman and CEO Ernest T. Weir. Ernest was 40 years her senior and was recently divorced with two grown sons roughly Mary's age.
Mary Hayward and Ernest T. Weir were married in December 1941, and together had one son, David Weir, born in 1944. She was later widowed in 1957, when her husband died at the age of 81.
On June 2, 1958 in Weirton, West Virginia, a public library called "The Mary Hayward Weir Public Library" was named in her honor with Weir cutting the ribbon in person.
On January 11, 1962, she married the Polish author Jerzy Kosinski after a romance of 18 months. Kosinski had emigrated from Poland in December 1957 to the United States. Weir and Kosinski met in the summer of 1960 in New York City, when the heiress hired the young Kosinski to catalogue her private library. Weir was a close friend of coffee heiress Abigail Folger, of the Folgers Coffee Company family, and it was through her husband Jerzy Kosinski that Abigail met her future boyfriend Wojciech Frykowski (Folger and Frykowski were savagely murdered in 1969 by the Manson gang).
Weir was known for both her never ending volunteer work in many different areas, as well as her extensive travels around the world.
She was also known to have battled many serious bouts of depression beginning as far back as 1950, and at times suffered from blackouts as a result of this. She also struggled with alcoholism for years.
In 1965, Kosinski dedicated his novel The Painted Bird to her, and it was at this time that she began to feel ill. Later in 1966, Weir divorced Kosinski, but she still remained a close friend. Mary was later diagnosed with a brain tumour, of which she died on August 1, 1968, aged 52 or 53.