Krzysztof Zygmunt Pac (Lithuanian: Kristupas Zigmantas Pacas) (1621–1684) was the Chancellor (1658–1684) of the Grand Duchy of Lithuania.
He was the brother of Michał Kazimierz Pac, the Great Lithuanian Hetman (1667–1682) who sponsored St Peter and St Paul's Church in Vilnius, a masterpiece of Baroque architecture. After their deaths, the influence of the Pac family deteriorated.
K. Z. Pac was an educated man. He studied in Kraków, Liège (now Belgium), and for eight years at the University of Perugia in Florence, Italy. When he returned to the commonwealth he obtained permission from Rome to establish a monastery for the Order of Camaldolese. The construction started in 1664. This monastery is now known as Pažaislis monastery and is considered to be one of the best examples of baroque architecture in the lands of present Lithuania.
In 1673 K. Z. Pac succeeded in passing a law stating that the convention of every third Sejm of the Polish-Lithuanian Commonwealth should take place in Hrodna, a city in the Grand Duchy of Lithuania. He was also appointed Vilkaviškis elder.
He was married to Klara Isabelle de Mailly (~1631/35-1685), an authoritative woman. Their first born son died at the age of eight days and they had no other children. Instead, K. Z. Pac helped to launch his nephew's political career; he later continued to sponsor construction of the Pažaislis monastery.
He, his wife and their son were all buried in the cemetery of Pažaislis monastery. Their grave was robbed and vandalized several times during the monatsery's eventful history. In 2003 they were properly reburied in a ceremony led by Kaunas archbishop Sigitas Tamkevičius.