The former MP Tam Dalyell has died at the age of 84 after a short illness.
He sat in the House of Commons from 1962 to 2005, representing West Lothian and Linlithgow for Labour.
Mr Dalyell became known for his formulation of the "West Lothian Question" about the role of Scottish MPs after the establishment of the Scottish parliament.
His family said in a tribute that he had made an enormous contribution and "devoted his life" to public service.
They said: "The family of Tam Dalyell are sorry to announce his death earlier today at the age of 84, after a short illness.
"Tam Dalyell devoted his life to public service in Scotland, in the UK, and beyond. He made an enormous contribution in many spheres.
"He will be much missed both publicly, and more importantly personally, by his family and many friends."
He won admiration from across the political spectrum as an honourable and principled member of parliament.
Falklands War
Mr Dalyell persistently questioned Prime Minister Margaret Thatcher over the sinking of the General Belgrano during the Falklands War.
He challenged her over the sinking of the warship during the conflict between Britain and Argentina - with the loss of more than 300 lives - and whether it had been necessary.
Labour leader Jeremy Corbyn said Mr Dalyell had been a "good friend and comrade".
"Tam was a titan of parliamentary scrutiny, fearless in pursuit of the truth. From Iraq to the miners' strike, he doggedly fought to expose official wrongdoing and cover-ups," he said.
"The title of his autobiography summed Tam up to a tee: 'The Importance of Being Awkward.'
"But he was much more than that: Tam was an outstanding parliamentarian, a socialist and internationalist, and a champion of the underdog, here and abroad."
PA
Former Prime Minister Gordon Brown said: "For four decades, Tam Dalyell was one of the truly great characters of Scottish political life.
"He was widely respected and admired for his insight, his integrity and his eloquence.
"My thoughts are with his family."
Scottish Labour leader Kezia Dugdale said: "The Labour movement has lost a giant. Tam Dalyell was one of the most influential MPs, writers and thinkers of his generation.
"Tam served the people of West Lothian tirelessly for decades through periods of great change. He truly was their champion. As Father of the House his wisdom was passed on to countless MPs, serving as a parliamentarian while Britain had eight Prime Ministers.
She added: "A man of peace and a man of principle, his legacy will live on in the Commons for decades to come.
"Our thoughts are with his family and many friends at this time."
Scottish Conservative leader Ruth Davidson added: "Tam Dalyell will be remembered as one of this country's greatest ever campaigning MPs.
"Throughout his long career, he championed a countless array of causes, giving voice to people who otherwise would not have been heard.
"He was unique - thoughtful, gracious, decent and utterly tenacious. All political parties today will mourn his loss while celebrating a great political life."
