Lady Sylvia Hermon mostly backed Labour in Westminster votes
Lady Sylvia Hermon, 54, is a former law lecturer who once worked with David Trimble at Queen's University Belfast.
She was a staunch supporter of his pro-Good Friday Agreement stance during his time as Ulster Unionist Party leader, and she was first elected as MP for North Down in 2001.
One of two new Ulster Unionists elected in 2001, Lady Hermon ousted the anti-Agreement unionist Robert McCartney, formerly the sole parliamentary representative of the United Kingdom Unionist Party.
She won with the support of the Alliance Party, which withdrew its candidate in her favour.
She was selected to fight the seat less than a month before the general election, after the previous prospective candidate - dissident assembly member Peter Weir, who later joined the DUP - was deselected after consistently opposing the UUP party line at Stormont.
David Trimble, now Baron Trimble of Lisnagarvey, was one of five Ulster Unionists to lose their parliamentary seat in the party's disastrous 2005 general election.
Lady Hermon was the only UUP MP to retain her parliamentary seat, taking 50.4% of the vote in North Down.
In the days following the election, Lord Trimble quit as party leader. A year later, he became a Conservative peer. He said his move to the Tories was
part of a "long-term ambition".
Sir John Hermon first met Lady Sylvia when she wrote a critical article
However, Lady Hermon had substantial ideological differences with her old friend, mostly voting with the Labour Party in Westminster.
It was a difficult time for Lady Hermon, as she was also nursing her husband Sir Jack Hermon, who was suffering from Alzheimer's disease.
Sir Jack was the chief constable of the RUC between 1980 and 1989, one of the most turbulent periods of the Troubles.
She first got to know him when he contacted her after she had written an article which criticised him.
died in November 2008,
after being ill for a number of years.
In February 2009, it was confirmed that the Ulster Unionists had forged a long-awaited electoral pact with the Conservative Party.
In May 2009, following months of speculation about her intentions, Lady Hermon said she could not see herself "standing under a Conservative banner".
She said she was elected as an Ulster Unionist and would serve under that mandate.
In October 2009, the Conservatives selected former Alliance Party member Ian Parsley as their choice to stand in North Down.
Lady Hermon finally quit the Ulster Unionists on 25 March, saying the gulf was too wide between herself and the party.