Gladys Moore Vanderbilt, Countess Széchenyi (August 27, 1886 – January 29, 1965), was an American heiress from the Vanderbilt family and wife of Hungarian Count László Széchenyi.

She was born Gladys Moore Vanderbilt in 1886, the seventh and youngest child of Cornelius Vanderbilt II and his wife Alice Claypoole Gwynne. Her father was the president and chairman of the New York Central Railroad and part of the prominent Vanderbilt family.

She grew up in the one of the Vanderbilt family mansion on Fifth Avenue in New York City and at their summer "cottage" called The Breakers in Newport, Rhode Island.^[1] She attended Miss Chapin's School in New York.^[2]

Her first cousin was Consuelo Vanderbilt, Duchess of Marlborough, who had married Charles Spencer-Churchill, 9th Duke of Marlborough.^[3]

One of her siblings was Reginald Claypoole Vanderbilt, who was the father of Gloria Vanderbilt, the mother of Anderson Cooper.

She inherited about $25 million (equivalent to almost $1 billion today) from her father's estate and a further $5 million from her mother's estate.^[4] She also inherited The Breakers. In 1948, as a widow, she leased The Breakers to the Preservation Society of Newport County for $1 a year. She continued to maintain an apartment in The Breakers by agreement until her death. In 1951, she donated her mother's iconic Electric Light dress to the Museum of the City of New York.^[5][6]

In 1913, there were rumors that she was going to leave her husband due to his financial woes,^[7] including gambling away all of her dowry.^[8]

In 1914, during World War I, she placed her palace in Budapest at the disposal of the army. Shortly thereafter, 600 reservists were quartered there, and she further intended to use the palace as a hospital.^[9][10]

On January 27, 1908, she married Hungarian Count László Széchenyi (1879–1938) in New York City.^[11][12] Their union was the most talked about and widely reported since her cousin Consuelo Vanderbilt's. The couple visited Hungary^[13] almost every summer with their five daughters:

• Countess Cornelia "Gilia" Széchényi de Sárvár-Felsövidék (1908–1958),^[3] who married Eugene Bowie Roberts (1898–1983), an heir of the Roberts family of Bowie, Maryland (a colonial family of Maryland), they had three children;
• Countess Alice "Ai" Széchényi de Sárvár-Felsövidék (1911–1974),^[14] who married Hungarian Count Béla Hadik (1905–1971), they had two sons;
• Countess Gladys Széchényi de Sárvár-Felsövidék (1913–1978),^[15] who married the half American English peer Christopher Finch-Hatton, 15th Earl of Winchilsea (1911–1950), they had two sons;
• Countess Sylvia Anita Gabriel Denise Irene Marie "Sylvie" Széchényi de Sárvár-Felsövidék (1918–1998), who married Hungarian Count Antal Szapáry von Muraszombath Széchysziget und Szapar (1905–1972), they had two children;
• Countess Ferdinandine "Bubby" Széchényi de Sárvár-Felsövidék (1923–2016), who married Austrian Count Alexander von und zu Eltz (1911–1977), they had two sons.

In March 1912, Countess Széchenyi's jewelries worth $200,000 was stolen from her town residence in Budapest, the detective afterward found the jewels in a motor car garage, where they had been hidden by being wrapped in a piece of newspaper behind a barrel. The countess promptly sent a $600 reward to the investigator. Upon learning of this, the Chief of Police issued an order for the money's return, stating that the police officer had fulfilled his duties and didn't need any further compensation.^[16]

Her sister Gertrude was married to Harry Payne Whitney, brother to Dorothy Payne Whitney, whose son Whitney Straight married Lord Winchilsea's sister, Lady Daphne Finch-Hatton.

Countess Széchenyi died in 1965. In 1972, the Preservation Society purchased The Breakers for $365,000 from her heirs.^[17] Her daughter, Countess Sylvia Szapáry, maintained a residence at The Breakers^[18] on the third floor until her death on March 1, 1998.

Through her eldest daughter, Cornelia, she was the grandmother of three – Gladys Vanderbilt Roberts (b. 1934), Cornelia Roberts (1936–1982), who married Count Hans-Heinrich von Coudenhove-Kalergi (1926–2004), and Eugene Bowie Roberts, Jr. (1939–2020). Through her daughter Alice, she was grandmother to Count László Hadik (1932–1973) and Count János Hadik (1933–2004). Through her daughter Gladys, she was the grandmother of Christopher Denys Stormont Finch-Hatton, the 16th Earl of Winchilsea (1936–1999) and the Hon. Robin Finch-Hatton (1939–2018). Through her daughter Sylvia, she was the grandmother of Count Pál László Szapáry (b. 1950) and Countess Gladys Vanderbilt Szapáry (b. 1952). Through her youngest child, Ferdinandine, she was the grandmother of Count Peter von und zu Eltz (b.1948) and Count Nicholas (Nicky) von und zu Eltz (1950–2012).^[19]