Former Labour Home Secretary Lord Merlyn-Rees has died at the age of 85 in hospital in south London.
Merlyn Rees was Northern Ireland Secretary under Harold Wilson
The Labour peer served under the governments of both Harold Wilson and James Callaghan.
He also held the post of Northern Ireland Secretary during his time on the Labour front benches of the 1970s.
Prime Minister Tony Blair said as well as being a leading figure in the party, the peer was "modest, generous, wise and loyal" and a personal friend.
Mr Blair said Lord Merlyn-Rees had won widespread affection, respect and admiration.
He was someone "whose advice I always valued and whose loyalty to Labour could never be questioned", the prime minister said.
Former Chancellor Lord Healey, who as Denis Healey served alongside Merlyn Rees in both the Wilson and Callaghan Cabinets, described the death of his former colleague as "a loss to the Labour Party and the country".
Lord Merlyn-Rees died on Thursday morning at St Thomas' Hospital in Lambeth. He had suffered several falls then lapsed into a coma from which he never regained consciousness, his family said.
Merlyn Rees served as MP for Morley and South Leeds and spent two and a half years in what was regarded as the cabinet's hottest seat in the early 1970s - Secretary of State for Northern Ireland.
He was appointed to it when Labour won power in 1974 and held it longer than any minister before him. He became home secretary in 1976.
BBC political correspondent James Landale said Merlyn Rees was a "hard-line" home secretary and a key figure of the 1970s.
Lord Merlyn-Rees once famously suggested vandals "needed an old-fashioned wallop", he said.
He took over the Northern Ireland post just as a short-lived attempt at a power sharing administration took place between Protestants and Catholics.
The BBC's Ireland correspondent Denis Murray said he would be remembered for his attempts at devolving power and phasing out internment among other things.
The son of a miner, Merlyn Rees was born in 1920 in south Wales, but was educated mostly in London.
After wartime service in the RAF, he spent 11 years teaching economics and history at Harrow Weald Grammar School where he had been a pupil.
He was an unsuccessful candidate in three parliamentary elections in Harrow.
He joined the Labour Party headquarters to organise the 1962 Festival of Labour and then, after a brief return to teaching, entered the Commons.
He was made a life peer when he left the Commons in 1992, changing his name by deed poll so that he could be called Lord Merlyn-Rees, rather than the more conventional Lord Rees.
He continued to be active in the House of Lords right up into his 80s, despite developing Parkinson's Disease.
He last spoke in the Lords in mid-December on the issue of terrorism.