Trần Lệ Xuân, more popularly known in English as Madame Nhu, was the de facto First Lady of South Vietnam from 1955 to 1963. She was the wife of Ngô Đình Nhu, who was the brother and chief advisor to President Ngô Đình Diệm. As Diệm was a lifelong bachelor and because she and her family lived in Independence Palace together with him, she was considered to be the first lady.

Ngô Đình Nhu was a Vietnamese archivist and politician. He was the younger brother and chief political advisor of South Vietnam's first president, Ngô Đình Diệm. Although he held no formal executive position, he wielded immense unofficial power, exercising personal command of both the ARVN Special Forces and the Cần Lao political apparatus which served as the regime's de facto secret police.