Jan Sergiusz Gajek (Belarusian: Сяргей Гаек, romanized: Siarhiej Hajek; born Jan Gajek on 2 February 1949) is the Apostolic Administrator of the Belarusian Greek Catholic Church which is a sui iuris (independent) Eastern Catholic Church on the territory of Belarus.^[1] It is in full communion with the Holy See.

He was born into a Polish Roman Catholic family in Łyszkowice, central Poland, and graduated from a local school and from a gymnasium.

In August 1967, Gajek joined the Congregation of Marian Fathers. Between 1967 and 1974, he studied at the Catholic University of Lublin. In the late 1960s, Gajek became engaged in activities of the exiled Belarusian clergy. He had contacts with the Belarusian cultural and religious centre in London, including bishop Ceslaus Sipovich and Robert Tamushanski. On 23 June 1974, he was ordained to the priesthood, and served for several years in a parish in Głuchołazy.

The following two years Gajek studied at the Theology Faculty of the Catholic University of Lublin. After that he was sent to Rome, where from 1978 to 1983 he studied at the Pontificia Instituto Orientale. In November 1983, Gajek became Doctor and returned to Poland. From 1983 to 1999, he worked at the Catholic University of Lublin.

In 1994, Pope John Paul II appointed Gajek Apostolic Visitor for Greek Catholics in Belarus. In 1996, Gajek became Archimandrite and corresponding member of the Pontifical Academy of Mary. In 1997, he became adviser of the Congregation for the Oriental Churches.

Gajek is author of numerous scientific publications on Christianity in the Slavonic East.

On March 30, 2023, Pope Francis erected the apostolic administration of Belarus for the faithful of the Byzantine rite and appointed him the first apostolic administrator.^[2][3]

• Father Gajek in 2008
• Father Gajek in 2012