Lord Bannside, better known as the Rev Ian Paisley, is in intensive care in Belfast with heart problems. Aged 85, he has been prominent in Northern Ireland politics for more than half a century.
Dr Paisley, pictured, a former Belfast First Minister and head of the Democratic Unionist Party, was admitted on Sunday. A statement on behalf of his wife, Baroness Paisley, said she "requests that the family's privacy be respected at this difficult time".
In recent years he made a dramatic turnaround, abandoning decades as a hardline rejectionist opposed to compromise to go into political partnership with Sinn Fein. In particular he formed a warm personal relationship with former IRA leader Martin McGuinness which helped transform the landscape and tone of Belfast politics.
Less than two weeks ago he preached his final sermon at the Martyrs Memorial Church in Belfast, the headquarters of the Free Presbyterian Church, which he founded in 1951.
He stepped down as moderator of the Church in 2008 and from elected politics last year. As well as leader of the DUP, he held the North Antrim seat at Westminster for 40 years. He was succeeded as an MP by his son Ian while he was followed as First Minister by his long-time deputy Peter Robinson.
Dr Paisley has had health concerns in the past, especially in 2004 when he was visibly gaunt at a political negotiating session held at Leeds Castle. He later acknowledged that he had been seriously ill, writing that he had "walked in death's shadow".
He appeared to make a good recovery from that bout, though a year ago he was taken ill in the House of Lords and required the attentions of paramedics. He was later fitted with a pacemaker at St Thomas's hospital in London.
He recently told his congregation that he intended to write his memoirs, promising: "I will be telling some stories that will make some people laugh and others blush."