The head of the Democratic Unionists at Westminster will be one of the favourites to take over as leader.
Nigel Dodds is North Belfast MP and has served in the past as a member of the Northern Ireland Assembly and minister in the Stormont Executive.
The married father-of-two has been an upholder of the fundamentalist unionist party’s stance on social issues, supporting evangelical preacher Pastor James McConnell after he was accused of anti-Islamic slurs.
He has also argued strongly against the introduction of same sex marriage.
Mr Dodds is DUP deputy leader and spokesman on reform, constitutional issues and foreign affairs.
The barrister was educated at Portora Royal School, Enniskillen and St John’s College, Cambridge. He also studied at the Institute of Professional Legal Studies at Queens University, Belfast.
He worked on the European Parliament’s Secretariat between 1984 and 1996, largely during former DUP leader Ian Paisley’s tenure as MEP.
In 1998 Mr Dodds was the youngest person ever to hold the post of Lord Mayor of Belfast City Council. In 1992 he was awarded the OBE for services to local government.
Arlene Foster, a Fermanagh South Tyrone Stormont Assembly member, has stood in for Peter Robinson as First Minister after he took a six-week hiatus in 2010 following a storm over his wife Iris’s affair and finances.
During recent political talks on paramilitarism as the powersharing government threatened to collapse, she also deputised as head of the administration.
The married mother is a lawyer from County Fermanagh who joined the Democratic Unionists in January 2004, just weeks after resigning from the rival Ulster Unionist Party.
As a child she had first-hand experience of the violence that engulfed Northern Ireland during the Troubles.
The IRA tried to kill her father, a part-time policeman in the Royal Ulster Constabulary (RUC), while she was a young schoolgirl - shooting him in the head while he farmed.
As a teenager in 1988, she survived a bomb which exploded under her school bus which was being driven by a part-time Ulster Defence Regiment soldier.
She was educated at Enniskillen’s Collegiate grammar and went on to study law at Queens University, Belfast.
She was a solicitor in Enniskillen and Portadown for 11 years, before devolution was restored to Northern Ireland in 2007.
In February 2008 she was named as the Parliamentarian/Assembly Member of the Year at the Women in Public Life Awards which were held in London.
Sammy Wilson, East Antrim MP, could be another leadership contender.
He has been a colourful presence in Parliament and the Assembly, known for his robust exchanges as Stormont finance minister and his unorthodox views on climate change as environment minister.
Mr Wilson has held public office since 1981, when he was first elected to Belfast City Council on which he served until February 2010, topping the poll at every election.
During his time on Belfast City Council, he twice served as Lord Mayor, in 1986/87 and 2000/01.
Another senior Democratic Unionist, Simon Hamilton, has enjoyed a meteoric rise under Peter Robinson’s leadership.
Born in 1977, the admirer of Margaret Thatcher and Ronald Reagan’s small government policies grew up in Comber near Belfast. He has a wife and children.
He graduated from Queen’s University Belfast with a BA in modern history and politics and a postgraduate bachelor of legal sciences degree.
He is health minister in the Stormont Assembly having previously served as finance minister.
Mr Hamilton is a moderniser keen to cut government waste.
He was a councillor on Ards Borough Council, in the east of Northern Ireland, from 2005 until 2011, representing Newtownards town.
Mr Hamilton recently announced far-reaching changes at the Department of Health including a shake-up in how health services are delivered.