Some believed (incorrectly) that the future Pope John Paul II would take the name Gregory XVII if elected.

A Canadian antipope Jean Gregoire de La Trinité, alias Jean-Gaston Tremblay.

Pope Gregory XVII is a name used by some sedevacantist organisations to describe three people regarded as the legal pope. All three are regarded by mainstream Roman Catholicism as antipopes.

The Spanish antipope Clemente Domínguez y Gómez (1946—2005), leader of the so-called Palmarian Catholic Church.

Giuseppe Siri whom some claimed was elected pope in 1958 and announced that his regnal name would be Pope Gregory XVII. (Siri refused to accept their claims and openly acknowledged popes John XXIII, Paul VI, John Paul I and John Paul II as legitimately on the See of Peter.)