The DUP's stance on a number of issues such as abortion and gay marriage has raised concerns among the Conservatives, fearful that it would harm the party's efforts to modernise, and engage with new audiences in recent years, relegating it firmly to right-wing politics.
Formed in 1971 by Ian Paisley, the party is now led by Arlene Foster.
Relations between the DUP and Sinn Fein broke down over the cash-for-ash controversy where people were essentially making money from the Renewable Heat Incentive by installing the wood pellet boilers - a scheme which DUP ministers oversaw. They reaffirmed this position on election night. "And she did not win", said another protester. At the age of eight, her father, a part-time policeman, was shot and injured by the IRA on the family farm. He was shot and crawled into the family home covered in blood but survived.
The DUP supports the renewal of the submarine-based nuclear deterrent, in common with the Conservatives.
Foster has said Theresa May is "well within political mainstream".
The DUP appointed him environment minister in Stormont in 2008. Both Foster and her deputy Nigel Dodds were invited to the Tory Party conference previous year.
Shock, surprise, relief; a tumultuous range of emotions were felt last night as the Labour party defied the pre-election polls by gaining a whopping 29 seats across the country, while the Conservatives lost 12; and now some people are getting angry.
The DUP wants no extension to Northern Ireland's limitations on terminations, which restrict the procedure to when a woman's life is at risk or there is a permanent or serious risk to her mental or physical health.
The strength of that deal looks set to be tested when the Commons meets next week, with Jeremy Corbyn vowing to try to bring down the Government by defeating Mrs. May in Parliament and insisting: "I can still be prime minister". But if Mrs. May is doing a deal with the DUP, that could make it harder to reach an agreement with Sinn Fein.
"Instead of peace we have confrontation by other means", he said.
"It didn't materialize then but we campaigned on the basis of a hung parliament two years ago".
Sir Jeffrey Donaldson, who defected to the DUP from the UUP at the same time Ms. Foster did in 2003, said his party would work with the Tories.
Office worker Christina Kelly, 38, described the result as "not exactly an ideal situation" but said it would likely focus more attention on Northern Ireland and particularly how Brexit would affect the region.
The DUP was also predicted to play the role of "Kingmaker" in the run-up to the 2015 general election - and was happy to talk up the possibility - before an unexpected Tory majority emerged under David Cameron.
"We fought this election on the importance of the Union and I think people really responded to that".
This minority government would be unable to pass laws and legislation without the votes of other parties that are not part of the government. Another potential problem is the planned restart of negotiations for power-sharing in the province.