The diminutive nun whose journey from a corner to the Ottoman Empire to the slums of India made her one of the most famous women in the world was regarded by many as a saint during her lifetime.
"Saint of the Gutters" and "Angel of Mercy," were among the sobriquets she picked up over the course of nearly four decades working with the wretched poor of Kolkata and building her Missionaries of Charity order into a global force.
But there was another school of thought. Australian feminist Germaine Greer called her a "religious imperialist" who preyed on the most vulnerable in the name of harvesting souls for Jesus.
But Teresa was always far more revered than reviled.
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Millions acclaimed her as an icon of Christian charity and a global symbol of anti-materialism and worthwhile self-sacrifice.
Her adopted homeland, India, took her to its heart. "It is natural for every Indian to take pride in Mother Teresa's canonisation," Prime Minister Narendra Modi said earlier this week.
On her death in 1997, Britain's Queen Elizabeth II predicted Teresa would "continue to live on in the hearts of all those who have been touched by her selfless love."
For long periods, she was plagued by doubts about the faith that drove her mission to provide comfort to the dying.
"There is so much contradiction in my soul," she wrote to the Bishop of Calcutta in a posthumously published 1957 letter.
"Heaven means nothing to me, it looks like an empty place."
Two years later, she wrote to a priest friend saying: "If I ever become a saint, I will surely be one of darkness; I will continually be absent from heaven - to light the light of those in darkness on earth."
Kosovar Albanian family in 1910 in Skopje, then part of the Ottoman empire and now the capital of Macedonia.
Her father, a businessman who was involved in the region's byzantine politics, died when she was eight.
By the time she was 12, according to biographers, Agnes was already a regular visitor to Catholic shrines and knew that she wanted to dedicate her life to missionary work.
At 18 she enrolled in an Irish order, the Sisters of Loreto, spending a brief period in Ireland learning English before her departure for India in 1929.
In 1979, her work in the Calcutta slums was rewarded with the Nobel peace prize. In her acceptance speech she made a fervent defence of her approach to helping the poor, which was by then coming under increasing critical scrutiny.
To those who said birth control was vital to combatting poverty, she replied that abortion was "direct murder by the mother."
To those who said her Order should promote development, she replied that she was a missionary, not a social worker.
But in his homily at her canonisation mass today, Francis hailed her as beacon for the world.
She was, he said, "an eloquent witness to God's closeness to the poorest of the poor."
Those who knew her best describe someone who loved fun, chocolate and ice-cream.
Father Brian Kolodiejchuk, a member of her Order who promoted her sainthood cause within the Vatican, told AFP Teresa would often be found bent over in laughter while discussing the day's events with fellow nuns.