Mordechai Hager (14 July 1922 (18 Tammuz 5682) – 16 March 2018 (29 Adar 5778), Hebrew: מרדכי הגר; Yiddish: האגער) was the rebbe (hereditary rabbinic leader) of the Hasidic sect of Vizhnitz for 46 years.

[3] In 1948, he arrived in the United States with his father-in-law and began serving as a rabbi of Vizhnitz Hassidim in Williamsburg, Brooklyn.

After his father's death in 1972, his two sons were appointed as rebbes of Vizhnitz as well, Moshe Yehoshua Hager in Israel, and Mordechai in the United States.

For example, he ordered his followers not to carry on Shabbos in Boro Park and Williamsburg, although the local Eiruv was approved by some of the city's rabbis.

He objected to eating ice cream at the end of the meal, due to halakhic doubts regarding the laws of the brokhoys before enjoyment and also for the purpose of celibacy of the pleasures of this world which he believed to be worthy of the "servant of God".