St. Faustina is called the apostle of Divine Mercy. She was a polish woman who received visions of Christ asking her to have the painting made of Christ as Divine Mercy, and to spread the devotion to Mercy in the Divine Mercy Chaplet, the Mercy Hour and others. She was born of a poor family in the village of Glogowiec in Poland. At age 7 she received her first vision of Christ drawing her to a holy life. She was only able to have a few years of education. Then as a young teen, she worked in other homes to help her parents who were very poor. As a teen, she felt called to the life of a nun, but her parents were against it. She tried to obey her parents, but when she was 18 she had another vision of Jesus who asked her how long must he wait. She eventually joined the Sisters of Our Lady of Mercy where, because of her lack of education, she worked the menial tasks at the convent, which she offer to God, as her mystic communion with our Lord increased. She was given the task to have the Lord of Mercy image painted, which was accomplished after one of the priest finally took her seriously. She wrote her diary after our Lord requested it in one of her visions. She died of tuberculosis at the age of 33. She was declared a saint, the first saint of the millennium by Pope John Paul II, also of Poland.
There are several more detailed biographies on line, as well as the detailed Diary which she wrote, that gives details of her life, her spirituality and visions and her mission. It can be found on line or purchased for a hard copy.
Here are some of the websites with details of her life and the Divine Mercy devotion:
Vatican description of her life and ministry
http://www.catholic.org/saints/saint.php?saint_id=510
http://www.faustina.ch/index_en.htm