Divine Mercy Sunday, celebrated on the Sunday after Easter Sunday, is a relatively new addition to the Roman Catholic liturgical calendar. Celebrating the Divine Mercy of Jesus Christ, as revealed by Christ Himself to Saint Maria Faustina Kowalska, this feast was extended to the entire Catholic Church by Pope John Paul II on April 30, 2000, the day he canonized Saint Faustina.
Known as the Apostle of the Divine Mercy, Saint Maria Faustina Kowalska of the Most Blessed Sacrament was a Polish nun who received frequent revelations and visits from Christ from 1931 until her death in 1938. The Divine Mercy Novena, the Divine Mercy Chaplet, and the Three O'Clock devotions were revealed by Christ to Saint Faustina.