Pope John Paul II has died at the age of 84, the Vatican announced Saturday, saying "The Holy Father died this evening at 9:37 p.m. in his private apartment."

The Pontiff's health had been in serious decline for about two months, following a Feb. 1 hospitalization for complications from the flu that included difficulty breathing. He became more gravely ill Thursday, March 31, when he developed a high fever due to a urinary tract infection, resulting in sepsis and heart and kidney failure.

The leader of the Roman Catholic Church also had suffered for a decade from Parkinson's disease. The progressive neurological condition left him increasingly frail in later years.

Born Karol Wojtyla on May 18, 1920, in Wadowice, Poland, he came to the papal office in 1978 and was the first Polish pope. His papacy was the third-longest in church history and was marked by unprecedented energy. John Paul made 104 journeys abroad, visiting 129 countries; canonized 482 saints; worked to ease political tensions worldwide; sought better relations with other religions; and became the most prolific writer in papal history. He also is credited with helping to end communism.

Tens of thousands of people gathered in St. Peter's Square to keep vigil for the ailing church leader, while Catholics and members of other faiths worldwide prayed for him. The week following John Paul's death will be devoted to public mourning and his burial, after which the process of choosing his successor will begin.

John Paul specified in a 1996 document, the Universi Dominici Gregis, that the conclave must begin 15 to 20 days after his death. During the conclave, the church's eligible cardinals will be sequestered until they have chosen a new pope. Among the issues facing the new pope will be bioethical dilemmas, the role of the church in China and Europe, a decline in the number of clergy, the balance of power within the church and relations with other faiths.