What did Mother Teresa do to become a saint?

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Mother Teresa, a Catholic nun who became renowned for her humanitarian work in India, was declared a saint on Sunday by Pope Francis.

Her name has become so synonymous with doing good that it has become a descriptor all of its own, taken to mean holiness and goodwill.

There are a number of criteria a person must fulfil in order to be canonised as one of the Catholic church's over 10,000 saints.

So what did the Albanian nun, originally named Agnes Bojaxhiu, do to earn the moniker 19 years after her death in 1997?

She was a servant of God

Mother Theresa at 85 (AP/PA)

One of the starter criterion for sainthood is for the person in question to dedicate their life to the service of God. Upon the person's death an investigation can be launched to verify whether their life met the standards expected.

If they do, the relevant bishop will ask the Congregation for the Causes of Saints for permission to begin a case for sainthood.

It is widely agreed that Mother Teresa did indeed dedicate her life to the service of God through helping others.

Mother Teresa talks to children (GG/AP)

At the age of 19 she joined an Irish order of nuns and was dispatched to India in 1929 to teach at a school in Darjeling.

Fifteen years later, the nun moved to Kolkata to help the destitute and founded the Missionaries of Charity a decade later. The organisation now has 4,500 nuns working an varied projects across the globe.

She lived a life of 'heroic virtue'

Mother Teresa meets Princess Diana (Bebeto Mattews/AP)

The next step is for the Congregation for the Causes of Saints to look into the life of the nominee. If they deem it of "heroic virtue", then the Pope can declare the individual "venerable".

Mother Theresa recieves the Nobel peace prize (Henrik Laurvik/AP)

Mother Teresa was not just revered in the Catholic community. In 1979 she won the Nobel Peace Prize for "work undertaken in the struggle to overcome poverty and distress in the world, which also constitutes a threat to peace".

This is not to say she was without critics. Some accused the care given at Missionaries of Charity centres to be substandard and unhygienic. In addition, some took against Teresa's opposition to contraception and abortion.

She has performed two miracles

(Arturo Mari/AP)

To become beatified, the person under consideration must have either died a martyr or performed a miracle which cannot be explained by modern medicine.

Mother Theresa's first miracle was the reportedly recovery of a woman from a stomach tumour overnight in Kolkata. Nuns at the Missionaries of Charity prayed for Mother Teresa to cure the woman. Following formal recognition of the miracle, Teresa was beatified in 2003 in a ceremony attended by thousands.

A tapestry of Mother Teresa hangs (Gregorio Borgia/AP)

To be canonised, officially named a saint, another miracle must have been performed after beatification.

In Mother Teresa's case, the miracle came in 2008 when a Brazilian man was reportedly cured of abscesses on his brain by placing a picture of Teresa by his bedside and praying to it.

Mother Teresa will be officially canonised in a Mass held by Pope Francis on Sunday.