So what does a United Nations Goodwill Ambassador do, and why are so many of them celebrities?
The ambassador title has been granted by the U.N. to a prestigious group of 190 do-gooder actors, athletes, musicians and writers from the U.S. and abroad who are passionate about issues such as combating HIV/AIDS, the plight of refugees and human trafficking.
The hope is that these famous names will amplify awareness of the world's most pressing issues.
Here are 10 standout celebrity ambassadors and their causes.
Angelina Jolie talks with children in the Dadaab refugee camp on the Kenya-Somali border. (Photo: Ho New/Reuters)
United Nations High Commissioner for Refugees
Jolie has traveled to remote refugee camps in Tanzania, Namibia, Pakistan and more, and has used her fame to call attention to the 20 million refugees in 120 countries that the U.N. assists.
Recently, because of her visit to a Bosnian refugee camp, the U.S. government made a sizable donation that will ensure the last 15 refugees left in the camp are given permanent homes.
In 2009, she spoke to Anderson Cooper about her work with the U.N.:
"There is a young boy I met who was about 15 who had been shot in the back and paralyzed. His whole family had been killed. He was completely on his own. Yet he had this really remarkable, unbreakable spirit, a spirit beyond anything I can imagine having."
David Beckham is greeted in Sierra Leone by 5-year-old Senyo, who suffers from malnutrition. (Photo: Getty Images)
United Nations Children's Fund
In 2008, Beckham went to Sierra Leone to draw attention to the issue of child mortality. In the West African country, 27 percent of children die before they are 5 years old, many from treatable and preventable causes.
Beckham went to South Africa in 2009 and met many children and mothers with HIV. He said of his visit:
"Today I met 25-year-old Tamara, who is living with HIV. Against the odds, she has become a counselor and support worker for other women in the same situation."
Beckham added that many women spoke openly to him about the stigma of HIV/AIDS. He said, "I hope that my visit gave them some hope and can send a message to others that stigma around this virus needs to end now."
Christina Aguilera is honored for her work combating hunger. (Photo: WireImage)
United Nations World Food Programme
Aguilera is a Goodwill Ambassador Against Hunger. In May 2010, she went to Haiti to see how food assistance is helping the country rebuild.
She said of why she wants to raise her voice to end world hunger, “A child dies every six seconds of hunger which is a huge statistic for me... After having my own child, I just had to be a part of it and do something about it and help change that situation."
The pop star is also the spokesperson for Yum! Brands World Hunger Relief Campaign, From Hunger to Hope and has helped raise more than $22.5 million for WFP and other agencies enabling them to provide more than 90 million meals to the hungry.
Julia Ormond testifies during a congressional hearing on human trafficking. (Photo: Getty Images)
United Nations Office on Drugs and Crime
Julia Ormond is advocating against human trafficking.
She said of becoming an ambassador:
"Taking on the U.N. role has taken me on a journey around the world that has exposed the degree to which enslavement is very much part of our world and is more prolific than ever. It is in agriculture, cotton, fishing and a lot of products that come into our world. It has been quite a horrific revelation for me."
This revelation led her to found the nonprofit Alliance to Stop Slavery and End Trafficking.
Kidman presents signatures to the U.N. secretary general to call attention to gender violence. (Photo: Lucas Jackson/Reuters)
United Nations Development Fund for Women
Kidman is raising awareness of the violation of women’s rights around the world and is putting a spotlight on violence against women.
This July, Kidman travelled to Haiti. After her trip, she said, "I saw first-hand how this humanitarian disaster is impacting women and girls. The lack of shelter and security makes them more vulnerable to violence, in particular sexual violence."
In Haiti, she visited a shelter for women and girls who had experienced or are at risk of sexual violence and where women leaders worked to ensure counseling, medical and legal services for the women. Kidman said, "This needs to be done on a large scale, and they need our support."
Don Cheadle and the Save Darfur Coalition hold a press conference at the U.N. about the genocide in Darfur. (Photo: WireImage)
United Nations Environmental Programme
Don Cheadle is calling attention to environment-based conflict and the ways we can all lessen the human impact on our planet.
When he became a Goodwill Ambassador in June 2010, Cheadle said:
"I would love it if we were able to live in a world which is in harmony with its environment. But it is money over people, money over environment, money over everything. We need to educate people on the environment and draw clear connections now—it is not disparate pieces, it really is a chain of life."
Shakira with kids in Bangladesh. (Photo: Getty Images)
United Nations Children's Fund
With UNICEF, Shakira has helped underprivileged kids around the globe by raising awareness and promoting education. She has advocated for children's rights in countries including Bangladesh, El Salvador and South Africa.
Shakira also started the Barefoot Foundation, which provides nutrition to more than 6,000 children in Colombia, and she's a member of the ALAS foundation that advocates for children across Latin America.
Annie Lennox performs to raise money for Nelson Mandela's HIV/AIDS '46664' campaign. (Photo: Andrew Winning/Reuters)
Joint United Nations Programmes on HIV/AIDS
Annie Lennox is speaking out for women and girls affected by HIV/AIDS.
In a UNAIDS statement, Lennox said, "If we are to end the cycle of human devastation triggered by the AIDS epidemic, we must address the rights of women and girls and challenge their second class citizen status, which puts them at greater risk of HIV."
She had been advocating for women and children well before being appointed to this position by the U.N.
In 2007, she launched the SING campaign to raise awareness about the epidemic.
Jet Li gives a speech on becoming a Goodwill Ambassador. (Photo: Stringer China/Reuters)
World Health Organization
As a WHO Goodwill Ambassador, Jet Li is raising awareness about the need for medical assistance after a disaster strikes.
Even before being appointed to the role in 2009, Li had been involved in the emergency response of the 2004 South Asian tsunami and earthquakes in China, and has set up programs for youth coping with psychosocial challenges.
When the earthquake hit in Haiti, Li urged citizens worldwide to aid the disaster victims in any way they could.
Nicolas Cage speaks at the U.N. Convention against Transnational Organized Crime in Vienna. (Photo: AFP/Getty Images)
United Nations Office on Drugs and Crime
Nicolas Cage is commited to fighting global threats including organized crime, arms trafficking, child soldiers and human trafficking.
In Vienna this October, Cage addressed a U.N. conference on fighting organized crime. He said:
"I met a young girl who had been the sex slave of a rebel leader and bore his child. I met a boy who was forced to kill his own sister. Yet I was also amazed by these children, and deeply humbled. So many of the children I met displayed incredible strength and resilience, and an almost incomprehensible capacity for forgiveness, of both themselves and others."
Cage has established a fund to help former child soldiers and has supported efforts to promote international arms control.