(CNN) She dedicated her life to helping the poor in India, performed several miracles and won a Nobel Peace prize in 1979.
Mother Teresa, the world famous nun needs little introduction, and her canonization on September 4 at the Vatican in Rome, is expected to draw huge crowds.
But what exactly is a saint and how does someone become one?
We take a closer look.
What is a saint?
A saint is a person who has lived a devout Catholic life, serving God and selflessly assisting people in need.
Saints act as role models and they're also believed to communicate with God on someone's behalf when a request for help is made in prayer.
Catholics believe a saint is someone who lived a holy life and who's already in heaven.
It's near impossible to figure out the exact number of saints. One well-known work called "Lives of the Saints" lists 2,565 Catholic saints, but that doesn't count thousands of others considered saints in other regions across the world.
The Catholic Church even has a feast, All Saints' Day, on November 1 to honor the countless saints who aren't formally canonized.
What steps do they have to take?
Most saints don't actively pursue sainthood.
Instead, they dedicate themselves to humanitarian tasks and devote themselves to God. In some cases, the Pope recognizes such goods deeds after the individual's death, first beatifying, then canonizing the person in question.
American saints and blesseds
Pope Francis canonized
St. Junipero Serra during his visit to the U.S. Serra is credited with founding several missions in California that were created to spread the Christian gospel to the native peoples of that part of North America. Some Native Americans oppose Serra's canonization; they say his work contributed to the oppression of their ancestors.
St. Frances Xavier Cabrini (1850-1917), known as Mother Cabrini, was the first American citizen to be canonized. The Italian-born nun founded the Missionary Sisters of the Sacred Heart of Jesus, and was canonized in 1946.
St. Marianne Cope was born Barbara Koob in 1838 in West Germany, but her family moved to the United States when she was an infant. She joined the Sisters of St. Francis in her early 20s and received the name "Sister Marianne." She is best known for her work with people afflicted with leprosy in Hawaii. She died in Hawaii in 1918.
Blessed Miriam Teresa Demjanovich was born in 1901 in New Jersey. She joined the Sisters of Charity in 1925. She is best known for her spiritual writings, which were published after her 1927 death under the title "Greater Perfection."
This is an undated photograph of St. Katharine Drexel. She was born in Philadelphia in 1858 and died in 1955. The heiress-turned-nun and founder of Sisters of the Blessed Sacrament is best known for devoting her life and fortune to starting schools in 13 states for blacks, missions for Native Americans in 16 states and 40 other mission centers and 23 rural schools. Pope John Paul II canonized her in 2000.
St. Rose-Philippine Duchesne was born in 1769 in France. She became a nun when she was 18, but her contemplative community was dispersed after the French Revolution. When she was 35, she joined the Society of the Sacred Heart of Jesus. When she was 49, she
sailed for what was then known as the New World, where she established her order's first house outside France and founded several schools. She died in St. Charles, Missouri, in 1852.
After a mass to celebrate the canonization of St. Mother Theodore Guerin, visitors look at the portrait of the French-born 19th-century nun at the Sisters of Providence of St. Mary-of-the-Woods in Terre Haute, Indiana, in 2006. She is best known for founding schools in Illinois and throughout Indiana. She is the patron saint of Indianapolis.
This is a statue of St. Isaac Jogues, thought to be the first Catholic priest to go to Manhattan, at New York City's St. Patrick's Cathedral. He is best known for his work as a missionary to the Huron and Algonquian nations in the area colonized by France in what is now the United States and Canada. Jogues, who died in 1646 after he was hit with a Mohawk tomahawk, is the patron saint of the Americas and Canada.
Blessed Francis Xavier Seelos was a German-born Redemptorist priest who pastored and preached in Catholic parishes and missions in Pennsylvania, Maryland, Louisiana, Michigan, Rhode Island, Wisconsin, Illinois, New Jersey and other states from 1844 until his death of yellow fever in 1867.
St. Elizabeth Ann Bayley Seton (1774-1821) was canonized as the first American-born saint in 1975. Seton converted to Catholicism after her husband's death. She founded the Sisters of Charity of St. Joseph, the first order of religious women in America, as well as several schools.
St. John Neumann was the first Redemptorist priest to profess his vows in the United States. The German-born priest became a U.S. citizen in 1848, at age 36. He is best known for establishing the first unified system of Catholic schools in Philadelphia.
This is a wooden statue of St. Kateri Tekakwitha, a 17th-century Mohawk woman who was canonized in 2012. She is best known for teaching prayers to children and working with the elderly and sick. St. Kateri died in 1680, just before her 24th birthday. She is the Roman Catholic Church's first Native American saint.
This is a statue of St. Damien de Veuster of Moloka'i, who was best known for his work with people suffering with leprosy in the Hawaiian islands. The Belgian-born priest ended up in Hawaii as a replacement for his brother, also a priest, who had been assigned to a mission in Hawaii but subsequently became too ill to travel. Upon arriving, the young priest offered to stay in the leper colony at Moloka'i permanently to help by building schools, hospitals, churches and coffins, according to the U.S. Conference of Catholic Bishops website. He worked closely with St. Marianne Cope. St. Damien ultimately contracted leprosy and died in 1889 at age 49. He is Hawaii's patron saint.
But you can't just be made a saint with the click of the Pope's fingers. There's a whole procedure -- described under the 'New Laws for the Causes of Saints' on the Vatican website -- that determines whether candidates really merit the honor, and the entire process can take several decades.
First up, a local church official examines a candidate's good deeds, life and writings for evidence of holiness and virtue. If they uncover enough material, they submit the candidate's case to the Vatican.
A group of cardinals and theologians of the Congregation for the Causes of Saints scrutinizes the case.
If the Congregation approves, the case is passed to the Pope. He decides if the candidate is "venerable" -- if they've sufficiently lived a life full of heroic Catholic virtue.
The next step is beatification -- recognition that an individual is in heaven. This status is granted when one of the candidate's miracles are verified posthumously. The miracle should be associated to prayers made to the candidate after their death from a person in need. If the prayer was granted, it proves that the candidate was able to communicate with God to conjure the miracle.
Miracles, however, are also scrutinized and deemed to be miraculous, only if they have no logical medical explanation.
The candidate is canonized and made a saint proper once a second miracle is verified posthumously.
How did it happen for Mother Teresa?
Remembering Mother Teresa
Mother Teresa, head of the Sisters of Charity, works with some of the lepers in Calcutta on December 7, 1971.
A 1960 portrait of Mother Teresa, the Albanian nun who dedicated her life to the poor, the destitute and the sick of Calcutta, India (later called Kolkata).
Mother Teresa in her hospital around the time she was awarded the Templeton Prize for Progress in 1973.
Mother Teresa delivers a speech after receiving her Nobel Peace Prize on December 10, 1979, in Oslo, Norway.
President Ronald Reagan and his wife, Nancy, bid farewell to the Mother Teresa at the White House on May 6, 1981.
Pope John Paul II and Mother Teresa wave to well-wishers in Calcutta on February 3, 1986.
First lady Hillary Rodham Clinton meets with Mother Teresa at the opening of the Mother Teresa Home for Infant Children on June 19, 1995, in Washington.
Diana, Princess of Wales, meets with Mother Teresa in New York in June 1997, months before the women died within days of each other.
Kosovo Albanian Catholics attend a religious service at the Blessed Mother Teresa Cathedral in Pristina on September 5, 2012, to mark the 15th anniversary of her death.
The nun was beatified in October 2003 by now deceased Pope John Paul II. He approved a first posthumous miracle. A 30-year-old woman in Kolkata said she was cured of a stomach tumor after praying to Mother Teresa.
A Vatican committee said it could find no scientific explanation for her healing and declared it a miracle.
In March 2016, Pope Francis announced that Mother Teresa would be declared a saint after recognizing a second miracle attributed to her.
A Brazilian man with multiple brain tumors was healed after loved ones prayed to her, the Italian Catholic bishops' association's official newspaper Avvenire reported.