Mary Katherine "Mary Kay" Fualaau (formerly Letourneau; January 30, 1962 – July 6, 2020), was an American teacher who pleaded guilty in 1997 to two counts of felony second-degree rape of a child. Letourneau was 34, and the child, Vili Fualaau, was 12 years old when she initiated the sexual abuse. He was her sixth-grade student at an elementary school in Burien, Washington. While awaiting sentencing, she gave birth to Fualaau's daughter. With the state seeking a seven and a half year prison sentence, she reached a plea agreement calling for six months in jail with three months suspended and no contact with Fualaau for life, among other terms. The case received national attention.

Shortly after Letourneau had completed three months in jail, the police caught her in a car with Fualaau. A judge revoked her plea agreement and reinstated the prison sentence for the maximum allowed by law of seven and a half years.  Eight months after returning to prison, she gave birth to Fualaau's second child, another daughter.  She was imprisoned from 1998 to 2004. Letourneau and Fualaau were married in May 2005, and the marriage lasted 14 years until their separation in 2019.

Letourneau died July 6, 2020, at her home in Des Moines, Washington, from colon cancer. She was 58. Fualaau and her family were at her side, despite their separation. A joint statement was made by the Fualaau and Letourneau families to commemorate her passing.  In her will, Letourneau left much of her estate to Fualaau.