Who's who at the RHI inquiry?
The DUP leader and former first minister headed the Department of Enterprise, Trade and Investment (Deti) when the RHI scheme was launched in 2012.
Subsidy tariffs were set too high and without a cap, leading to costs spiralling out of control.
Mrs Foster described it as her "deepest political regret", but strongly denies claims by Jonathan Bell – her former party colleague and successor as enterprise minister – that she ordered him to keep the scheme open.
- Arlene Foster lays blame for oversights at door of her civil servants
- Personal and political regrets but 'difficult to see what I could have done differently'
- 'I was not made aware' of vital RHI information
- Foster: did not sign blank cheque for RHI scheme
- Foster: I did not prevent note-taking over RHI scheme
- RHI scheme was not a personal priority, Arlene Foster tells inquiry
- Arlene Foster rejects any link between RHI and DUP supporters
Succeeded Mrs Foster as Deti minister in May 2015 and remained in post until May 2016 when RHI costs became a problem.
The former DUP Strangford MLA alleged two DUP special advisers (Spads), Timothy Johnston and Andrew Crawford, intervened to delay the introduction of cost controls in autumn 2015 – a period when there was a spike in applications to the already overstretched scheme.
He claimed Mrs Foster "overruled" his bid to finally close the botched scheme in early 2016.
- RHI Inquiry Live, Day 1: Jonathan Bell claims he was told of two DUP ministers' 'sexual misbehaviour'
- RHI Inquiry Live, Day 2: Bell claims Arlene Foster 'instructed' him to keep botched scheme open
A former barrister, he was Mr Bell's special adviser at Deti.
Mr Bell alleged Mr Cairns told him that other DUP Spads were not allowing the RHI scheme to be closed in September 2015.
Mr Bell said he believed Mr Cairns saw himself as working for the other Spads and not him as minister.
But Mr Cairns has accused Mr Bell of bullying, swinging a punch at him and trying to break his finger – claims Mr Bell denies
- RHI Inquiry Live: Timothy Cairns gives evidence
- Cairns claims Timothy Johnston 'involved in cost control delays'
- Timothy Cairns: Jonathan Bell 'ordered out of pub during Stormont trip to New York
- Timothy Cairns explains 'party narrative' text message
He became permanent secretary at Deti in 2014 and was in the post when the RHI scheme's massive overspend became clear.
Mr McCormick told the RHI inquiry that Mr Cairns told him Mr Johnston, another DUP Spad, was involved in the decision to delay cost controls.
In January, it was announced that Mr McCormick was being appointed as Director General of International Relations for Brexit amid the absence of an executive.
- RHI Inquiry Live, Day 1: 'The baton was dropped' senior civil servant says
- RHI Inquiry Live, Day 2: Civil servants rowed over problems with scheme
After being a special adviser to Ian Paisley and Peter Robinson, Mr Johnston became a Spad to Arlene Foster when she took on the role of first minister in January 2016.
He was accused by Mr Bell of not allowing the RHI scheme to close in early autumn 2015, but he has rejected that allegation.
Following the collapse of the Stormont executive over the RHI scandal in early 2017, he later became chief executive of the DUP.
- Timothy Johnston 'involved in cost control delays'
- DUP spad mocked Jonathan Bell after he 'cried on Peter Robinson's shoulder'
- Peter Robinson says senior Spad did not have his authority to act on RHI
- Timothy Johnston appointed as DUP chief executive
From Beragh in Co Tyrone, he was Spad to Mrs Foster in Deti when the botched RHI scheme was introduced, and was later a Spad to former DUP agriculture minister Michelle McIlveen.
He quit his Spad role in January 2017 after Mr McCormick told a Stormont committee hearing that he understood influence was being exerted by Mr Crawford to keep the scheme running at a high tariff level.
He denied the allegations and any wrongdoing. However, at the RHI inquiry, he accepted it was "inappropriate" to have shared RHI cost control plans with family members months before they were introduced. He is still employed by the DUP, doing part-time advisory work.
- Arlene Foster's spad leaked confidential government documents to business associates
- DUP spad told officials he was resigning to campaign and didn't mention RHI allegations
- Andrew Crawford provided Moy Park with 'inside information'
- Andrew Crawford didn't know RHI subsidy was incentive to 'burn to earn'
- DUP adviser should have 'dug deeper' ahead of RHI scheme launch
- Arlene Foster would not have signed off botched scheme if information on alternatives was correct
- DUP spad's 'greatest regret' was not reading key RHI report
As interim head of the Northern Ireland Civil Service (HOCS), he is effectively the man in charge of running Stormont departments in the absence of devolved government.
He was the lead civil servant in Deti when it introduced the flawed RHI scheme in 2012.
Mr Bell alleged to the RHI inquiry that Mr Sterling feared the energy scheme controversy would cost him his chance to become HOCS.
- David Sterling feared RHI would damage his career, Jonathan Bell claims
- David Sterling says Civil Service 'looks foolish for having not spotted the risk' involved
- Head of civil service says more credence should have been given to concerns
- Concern over 'scandalous' admission that some Stormont meetings were not minuted