Click on the names above for more details.
Role: Prime minister from 1997 to 2007. Seen as the most important witness.
Why is he involved? He is the man who took the UK to war in Iraq after persuading MPs that Saddam Hussein had weapons of mass destruction and was a threat to Britain.
He is likely to be asked whether the invasion was necessary and legal. He will probably appear before the panel early in 2010.
Role: Chancellor from 1997 to 2007 and current prime minister.
Why is he involved? He was a key member of Tony Blair's government and the man in power when the UK ended its combat operations in Iraq earlier this year.
He has indicated his willingness to appear before the committee.
SIR JOHN CHILCOT
Role: Iraq Inquiry chairman, privy counsellor and retired senior civil servant.
Why is he involved? Has been asked to look into the decisions made over the invasion of Iraq and determine "the lessons that can be learned".
He was a member of the 2004 Butler Inquiry into intelligence gathered by the government in the lead-up to the war.
SIR JEREMY GREENSTOCK
Role: UK permanent representative to the United Nations from 1998 to 2003.
Why is he involved? He was a key figure as the UK and US tried unsuccessfully to push for a second UN resolution explicitly authorising military action against Iraq if it did not comply with UN weapons inspection demands.
SIR DAVID MANNING
Role: Tony Blair's former chief foreign policy adviser.
Why is he involved? He was seen as an important figure in the development of the government's decision to go to war.
He will be expected to give insights to the inner workings and thought processes in Downing Street.
SIR CHRISTOPHER MEYER
Role: UK ambassador to Washington from 1997 to 2003.
Why is he involved? Is likely to face questioning over US-UK discussions relating to claims, made ahead of the war, that Saddam Hussein's regime possessed weapons of mass destruction.
SIR JOHN SCARLETT
Role: Chairman of the Joint Intelligence Committee, which oversees MI5, MI6 and GCHQ, from 2001 to 2004.
Why is he involved? His committee compiled the controversial dossier on the alleged threat posed by Iraq and its weapons of mass destruction in the lead-up to the war.
Role: Foreign secretary from 2001 to 2006.
Why is he involved? He was an important figure as the UK and US pushed the UN to back an invasion of Iraq. He was also closely involved in trying to persuade other countries to support this.
He is likely to be asked about dealings with the Iraqi regime which took power following the defeat of Saddam Hussein.