From Friedman to Obama: Controversial Nobel laureates

One of the most contested Nobels ever awarded went to the German scientist Fritz Haber. He won the chemistry prize in 1918 for inventing a method to synthesize ammonia - crucial for producing fertilizers that would revolutionize food production globally. But Haber was also known as the "father of chemical warfare" for developing toxic chlorine gases used in trench warfare during World War I.

Another German scientist, Otto Hahn (center), won the Nobel chemistry prize in 1945 for discovering nuclear fission. Although he never worked on the military application of his finding, it led directly to the development of the nuclear bomb. The Nobel committee had wanted to give Hahn the prize in 1940, but in the end he received it in 1945 - months after the atom bombs hit Hiroshima and Nagasaki.

Swiss scientist Paul Müller was honored in 1948 with the Nobel medicine prize for discovering that DDT could kill insects that spread diseases such as malaria. The pesticide's application during World War II and beyond saved millions of lives. But environmentalists later argued that it posed a threat to human health and wildlife. There's currently a global ban on the agricultural use of DDT.

With its implicit and explicit political statements, the Peace Prize is perhaps the most contentious of the Nobel awards. In 1935, the German pacifist Carl von Ossietzky was honored for exposing Germany's secret rearmament. Two Nobel committee members resigned over the decision. Ossietzky had been imprisoned for treason, and an outraged Hitler accused the committee of meddling in German affairs.

The decision to give the peace prize to US Secretary of State Henry Kissinger and North Vietnamese leader Le Duc Tho in 1973 was heavily criticized. Two Nobel committee members resigned in protest. The prize recognized efforts to reach a ceasefire in the Vietnam War, but Tho rejected the award, while Kissinger sent an envoy to accept it for him. The war continued for another two years.

Free market advocate Milton Friedman is one of the most controversial recipients of the Nobel economics prize. The award in 1976 caused international protests, mostly by the left, over Friedman's association with the Chilean dictator Augusto Pinochet. Friedman had visited Chile a year earlier, and protesters argued that his theories had inspired a regime that tortured and disappeared thousands.

The peace award shared by Palestinian leader Yasser Arafat, Israeli Prime Minister Yitzhak Rabin and Israeli Foreign Minister Shimon Peres in 1994 was intended to push the Middle East peace process forward. Instead, talks collapsed and Rabin was assassinated by an Israeli nationalist a year later. One Nobel committee member stepped down over the decision, calling Arafat a "terrorist."

Mayan indigenous rights campaigner Rigoberta Mechu won the peace prize in 1992 for "her work for social justice and ethnocultural reconciliation." She later attracted controversy when her memoirs were alleged to be partly fictitious. The comprehensive account about the genocide of the indigenous Guatemalans had brought her to fame. Nevertheless, many argued, she was no less deserving of the award.

Many were surprised when Barack Obama won the Nobel Peace Prize in 2009 - including the US president himself. Less than a year into his first term, Obama was honored "for his extraordinary efforts to strengthen international diplomacy and cooperation between peoples." Critics, and some Obama supporters, said the award was premature and came before he'd had a chance to make a real impact.

In 2011, the Nobel medicine prize went to Jules Hoffman, Bruce Beutler and Ralph Steinman for their discovery of a new immune system cell. The only problem was that Steinman had died of cancer days earlier. According to the rules, recipients cannot receive awards posthumously. In the end the board gave Steinman the award anyway, saying it had no knowledge of his death at the time.

Nobel Prizes have proved controversial both because of who has received them and who has been denied them. Gandhi, the leader of India's peaceful independence struggle, was nominated five times but never won. In 2006, Geir Lundestad of Norway's Nobel Committee said: "The greatest omission in our 106 year history is undoubtedly that Mahatma Gandhi never received the Nobel Peace prize."