YVO DE BOER
Role: Executive Secretary of the United Nations Framework Convention on Climate Change
About: Mr de Boer was appointed to the executive secretary position in August 2006 but has been involved in climate change policies since 1994.
He helped to prepare the position of the EU in the lead-up to the Kyoto negotiations. Earlier in his career, Mr de Boer worked for the United Nations Human Settlements Programme.
Mr de Boer is Dutch and was born in 1954.
Copenhagen outlook: To secure a political agreement in Copenhagen that can be transformed into a legally-binding treaty soon after the conference.
The US must commit to an agreement that can be approved by the Senate.
What he says: "A successful agreed outcome needs to capture a level of ambition that is commensurate with the scale of the problem."
LUMUMBA STANISLAUS-KAW DI-APING
Role: Ambassador and Deputy Permanent Representative of Sudan to the United Nations in New York and chair of the Group 77 and China
Will not settle for a politically-binding agreement. Says it is crucial for developing nations to come away with a legally-binding treaty.
Developing nations need funding for mitigation and adaptation efforts. He says the financial contributions by rich countries has to be an amount significant enough to lead to "rapid, sustainable development and industrialisation of developing countries, in particular Africa".
What he says: "A weaker (Kyoto) deal is a deal that is at the cost of our existence."
Role: Denmark's climate minister and president and chairwoman of the Copenhagen conference
About: Ms Hedegaard was appointed climate minister in 2004. She is a conservative politician who was first elected to Denmark's parliament in 1984 and was at the time the country's youngest MP.
She left politics in 1990 for journalism until she was recruited to her current position by Anders Fogh Rasmussen, the previous prime minister.
Ms Hedegaard is Danish and was born in 1960.
Copenhagen outlook: A politically-binding treaty with a set deadline for a legal draft is possible at Copenhagen.
Developed countries must come up with specific targets for greenhouse gas emission reductions as well as financial contributions.
What she says: "Every positive announcement will improve our chances of staying below the two degrees Celsius target."
Role: US special envoy on climate change
About: Mr Stern was appointed by Secretary of State Hillary Clinton on 26 January 2009. He has worked extensively in Democratic administrations, including most recently advising Ms Clinton during her 2008 presidential campaign.
Mr Stern served as Staff Secretary during the Clinton administration. From 1997 to 1999 he coordinated the administration's initiative on global climate change, acting as senior White House negotiator for the Kyoto Protocol.
Mr Stern is American and was born in 1951.
Copenhagen outlook: Only a politically binding and Senate-approvable agreement can be reached in Copenhagen.
Developed countries must provide financing for climate change adaptation and mitigation in developing nations.
What he says: "An interim, operational deal is not meant to be seen as a substitute for a real agreement."