Video: Who are the five DUP special advisers at the centre of the RHI storm?
A special adviser to former First Minister Arlene Foster and the DUP's director of communications in the years when the party squared up to David Trimble's Ulster Unionists, Timothy Johnston has had the ear of three former party leaders.
A former accountant, he was previously a member of the Ulster Unionists.
Involved in the negotiations that led to the restoration of power-sharing in 2007, he is said to have had a particularly close relationship with Peter Robinson.
The family of Ian Paisley blamed Mr Johnston for a critical survey carried out in 2008 amongst DUP MLAs and MPs of his leadership, months before Mr Paisley stepped down as First Minister and party leader.
Mr Johnston said the claim was regrettable and inaccurate.
Retained as a special adviser under both Peter Robinson and Arlene Foster, he is paid the maximum annual salary of £91,809.
During Monday's sitting of the Assembly, suspended DUP MLA Jonathan Bell used parliamentary privilege to accuse him of being one of the two Spads who moved to block the closure of the RHI scheme, a claim denied by Mr Johnston.
Mr Johnston said he has no connection to the scheme and has never sought to keep the scheme open, and although he has two brothers-in-law in the poultry industry, neither have links to RHI.
He is married to a sister of John Robinson, another DUP special adviser who has also been the subject of similar accusations by Mr Bell.
A DUP statement branded Mr Bell's allegations as "outrageous, untrue and unfounded mud-slinging".
Also named by Jonathan Bell during Monday's Assembly sitting, John Robinson is a special adviser at the Department for the Economy.
He was the DUP's director of communications until June last year, shortly after the most recent Assembly election.
Mr Bell alleged that Mr Robinson was one of two DUP advisers with "extensive interests in the poultry industry".
Having initially stated that his family farm has chicken houses which are not recipients under the RHI scheme, Mr Robinson later added that his father-in-law is a claimant.
Mr Robinson initially said: "I have no personal interest in the poultry industry. Two of my brothers are poultry farmers but they have no connections to RHI."
On Tuesday, Mr Robinson said that some months before he got married, his father-in-law purchased two boilers for his poultry business.
He said he did not discuss RHI with his father-in-law and that neither he, nor his wife, had any role or benefit in his in-laws' farming business.
Mr Robinson stressed he had never advised anyone to join RHI and added that neither he or his wife had any direct involvement with the business or RHI.
He said his father-in-law joined the scheme before he started to work directly with Mr Hamilton, who is currently looking at options to curtail its cost.
Mr Robinson said on Wednesday that he was stepping aside from any involvement in the RHI scheme to avoid the "accusation or perception of a conflict of interest".
Up until yesterday, Mr Crawford was a spad in the office of the agriculture minister, Michelle McIlveen, having previously worked as an former adviser to Arlene Foster in her roles as both enterprise and finance minister.
His resignation as a special adviser was announced yesterday by Mrs Foster.
A farmer from Beragh, Co Tyrone, Mr Crawford was a special adviser to Mrs Foster at the time she launched the botched initiative back in 2012.
A former employee of the Ulster Farmers' Union, Mr Crawford also worked as an assistant to Jim Allister during his time as a DUP MEP.
The Irish News revealed that Mr Crawford's brother, a poultry farmer, is a recipient under the RHI scheme.
The DUP spad has been accused by Jonathan Bell of preventing the closure of the scheme, a claim he denies.
On Wednesday, senior civil servant Andrew McCormick told an Assembly committee that while he did not have any direct evidence, he believed that Mr Crawford was the person who influenced the decision to keep the scheme open.
Mr Crawford said he would only have offered "informal advice" on the basis of his experience and insisted that he did not attempt to prevent the scheme's costs being curbed.
The first Spad to be confirmed as having been a beneficiary of the scheme, Stephen Brimstone left his £91,809-a-year position in November in order to pursue "opportunities in the private sector".
In December, Arlene Foster confirmed that he had been a recipient of payments, but neither the DUP nor Mr Brimstone have disclosed how much he has received or when he signed up.
In 2013, Mr Brimstone became embroiled in controversy when he was accused of telling Jenny Palmer, then the DUP's representative on the Housing Executive board, to change her vote in relation to a contract involving maintenance firm Red Sky, which later went bankrupt.
He denied any wrongdoing and the incident resulted in Ms Palmer defecting to the UUP.
Mr Brimstone was then promoted to the office of the first and deputy first minister, and served under both Peter Robinson and Arlene Foster.
The Irish News also revealed that Mr Brimstone's brother, Aaron, who runs a karting business in Co Fermanagh, is an RHI claimant.
No longer employed by the DUP, Timothy Cairns was the special adviser to former enterprise minister Jonathan Bell.
A former barrister, Mr Cairns worked as a spad in OFMDFM during Peter Robinson's time in office.
He was appointed as spad to Mr Bell in May 2015 when he became enterprise, trade and investment minister.
According to Mr Bell, Mr Cairns told him in September 2015 that his plans to curb the tariff on the RHI scheme were "not being allowed" by other DUP spads.
Mr Cairns, who left his spad post when Mr Bell was not re-appointed as a minister in May last year, has said that decisions about the scheme were ultimately up to the minister to take.
He is now employed as the director of the Community Transport Association for Northern Ireland and Wales.
The Irish News reported on Wednesday that Mr Cairns has been appointed to the board of cross-border business body InterTradeIreland by the DUP.
Spads, not spuds: