Dublin-born charity worker Margaret Hassan moved to Iraq 30 years ago, and began working for Care International soon after it began operations there in 1991.
Mrs Hassan warned that war in Iraq could cause a humanitarian crisis
When she was kidnapped, she had been head of the charity's operations in the country for some 12 years.
Married to an Iraqi, Mrs Hassan has Irish, British and Iraqi nationality.
Her friend Felicity Arbuthnot, a film-maker who has travelled to Iraq to document Mrs Hassan's work, described her as "an extraordinary woman".
"She is one of those slender people with a spine of steel," she said.
"She stayed there through the 1991 war, the bombings last year, all the horrors of the embargo.
"She has tremendous presence. If
there is anybody who can build a rapport with whoever these people are, she
will," Ms Arbuthnot said.
She said she had once travelled with Mrs Hassan to a water sanitation plant in a poor area of Iraq and seen her effect on the local people she was helping.
"A crowd gathered and tiny children rushed up and threw their arms round her
knees, saying, 'Madam Margaret, Madam Margaret,' and everywhere she went, people just beamed.
"She was so loved and everybody was so open with her and this is what makes
it so extraordinary."
Robert Glasser, chief executive of Care Australia, said: "It is important to note that she has been providing humanitarian relief to the most needy Iraqis in a professional career spanning more than 25 years.
"She has been on the ground helping the poor in Iraq for over 25 years."
Mrs Hassan warned MPs shortly before last year's war that Iraq could face a humanitarian catastrophe in the event of a conflict.
She said UN sanctions had left the Iraqi people in a worse situation than they had been at the end of the first Gulf War in 1991.
"The Iraqi people are already living through a terrible emergency," she told a House of Commons briefing.
"They do not have the resources to withstand an additional crisis brought about by military action."
Mrs Hassan chose to stay in Iraq during the war, and told the Newcastle Journal on the eve of the conflict that she was "sad" Britain was taking part.
She added she did not fear being targeted in revenge attacks by Iraqis.
International relief and development charity Islamic Relief, based in Birmingham, joined calls for Mrs Hassan's safe release.
She spoke to its members about Iraq in 2002, before the war, describing how a formerly prosperous nation had been systematically reduced to poverty.
Islamic Relief spokesman Ideel Jafferi said staff prayed for her after her kidnap.
Care International is the world's largest humanitarian relief agency, with a presence in 72 countries.
It has focused efforts in Iraq since the war on providing emergency relief and medical aid, and restoring access to clean water.
More than 30 staff, all Iraqis, work in its Baghdad office.