However, increasingly in her last decade, the image of Mother Teresa as a sign of contradiction in a materialistic and individualistic consumer world, an icon of courage and selflessness, was questioned. Her preference for prayer over medicine for treating the sick was highlighted by critics like the writer Christopher Hitchens in the 1994 television series and 1995 book The Missionary Position. Her refusal to move beyond feeding the poor to ask why they had no food to eat frustrated aid workers and fellow religious helpers. And her idiosyncratic approach to book-keeping - her order never kept accounts - and her willingness to take funds and awards from unsavoury characters like the Duvaliers in Haiti caused raised eyebrows.
It was characteristic of her steely determination that Mother Teresa never once in her last years let outside opinions deflect her from her primary purpose - giving practical expression to the love of God through caring for the sick, the needy and the dying all around the globe. Whether she was being feted by world statesmen or denounced by her critics, she stuck unflinchingly to the simple mission that had inspired her since childhood, utterly convinced that God's hand was guiding her.
Born Agnes Gonxha Bojaxhiu in 1910 in Skopje in Serbia, she was one of three children of well-to-do Albanian parents. From an early age she felt a twin calling - to the religious life and to India. In 1928 she joined the Irish-based Loreto Sisters and found herself teaching geography and history in their schools in Darjeeling and Calcutta.
After taking her final vows in 1937, she was appointed head of St Mary's, a Loreto school for local Bengali children in Calcutta. It adjoined the order's smart boarding school for the daughters of colonial officials and this juxtaposition made Sister Mary Teresa of the Child Jesus - as Agnes had become - uneasy.
On 10 September 1946, she experienced what she later described as "a secondary calling," to go out into the slums of Calcutta and work with the poorest and most needy. The date is celebrated as Inspiration Day by the Missionaries of Charity, the religious order she founded in 1950 to promote this vocation.
At first the church authorities tried to persuade her to abandon her new vision, but she knew that without the status of a nun she would never attract helpers. She stuck to her guns and, not for the first time in the years ahead, the ecclesiastical bigwigs yielded. In 1954 she opened Nirmal Hriday - Place of the Pure Heart - a home for the dying. A year later came Shishu Bhavan, the first of the order's many children's homes. By 1968 the Missionaries of Charity had established a base in Rome in response to an appeal from Pope Paul VI and they rapidly spread to all five continents. By 1995 there were 537 houses in 137 countries.
Mother Teresa ran her order like the old-fashioned headmistress she had once been. She was single-minded and would brook little dissent. When the lay support group, the Co-Workers of Mother Teresa, became too assertive, Mother Teresa closed it down. Talk of retirement in the late 1980s was quietly dropped after she found she could not relinquish the reins of power despite often delicate health. But she worked hard - if not always successfully - to dispel any cult of personality that surrounded her, insisting that all credit should go to God. In accepting the 1979 Nobel Peace Prize, she said: "Personally I am unworthy. I accept it gratefully in the name of the poor."
The success of the Missionaries of Charity in drawing in funding for their ever-increasing global network of projects and in attracting vocations was a testament to the magnetic power of Mother Teresa's vision. With many of Catholicism's religious orders struggling to find new recruits, the Missionaries of Charity is growing apace.
At a time when aid from the developed world to poorer nations was increasingly politicised and - often as a consequence - discredited and misdirected, Mother Teresa and her order have become for many individual donors an unimpeachable avenue for doing good and making a difference.
Mother Teresa enjoyed a close working relationship with Pope John Paul II. Though she endorsed his anti-contraception, anti-abortion gospels in every country where she travelled, she managed by and large to stand apart from the theological and moral disputes that divided her Church.
Small in stature and personally unassuming, Mother Teresa was never anything less than bold and decisive in promoting her own vision of God's love. When the British Prime Minister, Margaret Thatcher, welcomed her to 10 Downing Street in 1989, Mother Teresa took the opportunity at a joint press conference to spell out in unmistakably critical terms the plight of London's homeless who relied on the Missionaries of Charity for food and blankets. Mrs Thatcher was visibly taken aback.
Sainthood in Catholicism is always a posthumous honour, but for many Mother Teresa was an exception. In her lifetime she was acclaimed as a living saint. In death, it is certain that official canonisation will follow the popular mood.