The winner of this year's Nobel Peace Prize will be announced Friday in Oslo. Here are portraits of top contenders for perhaps the world's most-watched award.

+ Ales Belyatsky, Belarus

Ales Belyatsky is the leading defender of human rights in authoritarian Belarus, keeping up his life mission from jail in a relentless battle of wills with the regime of President Alexander Lukashenko.

Detained since August 2011, the director of the Vyasna (Spring) rights group was sentenced to four and a half years in a prison camp on tax evasion charges in November, with the court also ruling to confiscate his property.

Founded in 1996, Vyasna grew to have representatives and offices across Belarus, helping victims of political repression during Lukashenko's 18-year rule and campaigning against the regime's use of the death penalty.

The 50-year-old is frequently placed in the punishment isolation cell while other inmates are told not to approach him. But his resilience remains intact.

"Everything is well," Belyatsky said in a letter from prison. "Right now I am exactly where a human rights defender should be during such a situation in the country."

+ Svetlana Gannushkina, Russia

Veteran Russian human rights activist Svetlana Gannushkina, 70, is the founder and director of Civic Assistance, which helps refugees forced from their homes by the conflicts that erupted after the collapse of the Soviet Union.

The group formed in 1990 has also worked to help labour migrants from ex-Soviet states who have moved en masse to big Russian cities in the recent years but often face horrific working conditions and rising xenophobia.

Through the Russian rights group Memorial, she set up the Migration and Rights network which provides legal assistance to migrants and refugees in 50 locations across the country.

Gannushkina taught mathematics at a Moscow institute for 30 years until 2000 before devoting all her energies to rights work. She began with helping the victims of the conflicts between Armenia and Azerbaijan in the late 1980s.

She was a member of the Kremlin rights council under former president Dmitry Medvedev but resigned from the body shortly after Vladimir Putin returned to the presidency for a third term.

+ Memorial, Russia

Human rights group Memorial, founded in 1989 in the final years of Soviet rule, has emerged as the most prominent fighter against rights violations in the sometimes violent world of Russia under President Vladimir Putin.

The group has led the way in exposing violations in Russia's restive Northern Caucasus, particularly in Chechnya which fought two bloody separatist wars with Moscow after the 1991 collapse of the Soviet Union.

Memorial has also been one of the few organisations ready to question the authorities' official interpretation of modern Russian history, which often glosses over the horrors committed under wartime tyrant Joseph Stalin.

Its crusading stance has come at a cost and its senior Caucasus researcher Natalya Estemirova was murdered in July 2009 after being abducted in Chechnya, a crime that has yet to be solved.

The group now faces new challenges for survival. Russia's parliament has passed a law requiring NGOs with foreign funding to carry the tag "foreign agent" while the government has terminated the operations of its backer USAID.

+ Sima Samar, Afghanistan

Sima Samar is a pioneering Afghan doctor and human rights activist who has endured death threats, war and the Taliban to battle tirelessly for women in Afghanistan.

Samar, 55, is best known for setting up the Shuhada Organisation in 1989, which runs four hospitals, 12 clinics, 60 schools and two shelters. It also creates jobs for tens of thousands of Afghan women and girls in Afghanistan and Pakistan.

During the 1996-2001 Taliban rule, Shuhada ran underground home classes for girls in Kabul. Its girls' primary schools were among the few at the time and its high schools the only ones for girls.

A former UN special rapporteur on the human rights situation in Sudan, she now chairs the Independent Afghanistan Human Rights Commission, the first body in her nation to monitor and investigate rights abuses.

Samar is a member of the Hazara ethnic minority, and in 1982 she became the first Hazara woman to graduate from medical school.

Last month, Samar won the Swedish Right Livelihood Award -- known as the "alternative Nobel" -- honouring those who work to improve the lives of others.

+ Yoani Sanchez, Cuba

Cuban blogger Yoani Sanchez, 37, for more than five years has dared to take direct aim in print at the Americas' only one-party Communist regime.

Her blog is not outlawed or illegal in Cuba, but since most Cubans (with average income under $20 a month) do not have Internet access, she is largely unknown at home while garnering awards and fame abroad.

With a wry, restrained style, the former language student has surged to the forefront of a new generation of cyber-challenges to Cuba's five-decade-old geriatric regime.

She calls her blog Generation Y -- after the Soviet-era generation around her age, many of whose parents gave their children exotic-sounding, Russian-inspired names starting with Y.

Her dispatches -- usually several articles a week -- and Tweets are a critical take on tough everyday issues that face Cubans -- the extreme economic hardship, the regime's inertia, and the desperation that often leads Cubans to risk their lives and leave the country illegally.

One of the interviews she gave to foreign media earned her an anonymous attack from Fidel Castro. He mentioned a "young Cuban woman" at the service of "the neocolonial press." She shot back with a blog post saying: "Some old instruments of the Soviet era just refuse to die."

+ Gene Sharp, United States

Gene Sharp literally wrote the book on non-violent revolution, credited most recently with serving as a how-to manual for the Arab Spring uprisings.

The 93-page "Dictatorship to Democracy: A Framework for Liberation" has been published in more than 30 languages since it was written in 1993 by the now 84-year-old political scientist at the behest of Myanmar activists.

"Primarily, I try to understand the nature and potential of non-violent forms of struggle to undermine dictatorships," explained Sharp in "How to Start a Revolution," a 2011 documentary about his life and work.

Born and raised in Ohio, Sharp -- the son of a Protestant clergyman -- studied political science and sociology in his home state and at Oxford University in Britain where, in 1968, he completed a doctoral thesis on the politics of nonviolent action.

Dubbed by some "the quiet American" for his soft-spoken manner, he has taught at the University of Massachusetts and Harvard. He also founded the Albert Einstein Institution, named after the Nobel prize-winning physicist and pacifist, in East Boston as a centre of research into nonviolent forms of political struggle.

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