As Britain reeled from the shock election result which saw the Conservatives lose their majority, attention turned to the party that will prop them up in the House of Commons.
Early indications showed Ms May had been forced to ditch election manifesto commitments, promise £1bn of extra spending and even lucrative new tax powers to Northern Ireland to secure the DUP's support.
Speaking after the formal announcement that the parties had reached a deal, DUP leader Arlene Foster said: "Our aim in these negotiations has been to deliver for all of the people of Northern Ireland and the support measures which we are announcing will be to the benefit of all our people."
But who is party leader Arlene Foster - the new power behind Theresa May?
The 46-year-old was almost killed when she was a teenager after the IRA targeted her school bus, being driven by a soldier in the Ulster Defence Regiment.
The former First Minister of Northern Ireland has served as the leader of the DUP since December 2015.
She became First Minister in January 2016 and served until Martin McGuinness resigned in protest at her “cash for ash” scheme in January 2017, resulting in the collapse of power-sharing.
Ms Foster faced accusations of mishandling over an ill-conceived renewable energy scheme which overpaid businesses for using green heating systems, costing taxpayers in excess of £490m.
Ms Foster led her party in the campaign for Brexit, the only party in the Stormont executive to campaign for Leave. She is against a hard brexit, to avoid any hard border with the Republic of Ireland and new customs operations.
Ms Foster opposes same-sex marriage and abortion, and has campaigned against both.
“I would not want abortion to be as freely available here as it is in England and don’t support the extension of the 1967 act,” she told The Guardian in 2016.
Ms Foster is a lawyer by training, and is married with three children.
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