Former SNP leader Gordon Wilson has died after a short illness, the party has confirmed.
Mr Wilson died in hospital at the age of 79.
First Minister Nicola Sturgeon has led tributes to him, saying he made an "immense" contribution to the success of the SNP, and that his loss would be "keenly felt".
Mr Wilson had worked as a solicitor before being elected as the MP for Dundee East in 1974, a seat he held for the next 13 years.
He was leader of the SNP from 1979 to 1990, before being succeeded in that role by Alex Salmond.
Ms Sturgeon said: "Gordon Wilson's contribution to the success of the modern SNP was immense and his loss will be keenly felt across our party. He was a fine and kind man, a loving husband, father and grandfather and a true patriot.
"From his early days promoting the case for independence on Radio Free Scotland to his 13 years of service as MP for Dundee East and 11 years as leader of the party, Gordon was a passionate advocate for Scotland at every level.
"He was at the centre of many lively and passionate debates through the 1970s and 80s over how independence would be achieved and continued to play a part in the independence debate right though to the referendum in 2014."
She continued: "Gordon was always forthright in his views and his commitment to seeing Scotland become an independent country was second to none. Even - perhaps especially - on those occasions when his views on tactics differed from mine, I always highly valued and appreciated his advice.
"My thoughts are with Edith and all of his family at this time. Gordon will be fondly remembered and sadly missed by all those who knew and worked with him in the SNP and across the country."
Mr Wilson is survived by his wife Edith, his daughters Margaret and Kate, and five grandchildren.
Mr Salmond said: "Not only was Gordon one of the masterminds of the SNP parliamentary breakthrough of the 1970s but he led the party through tough times in the 1980s. Holding his Dundee seat in 1979 and 1983 was crucial in retaining the credibility which allowed the SNP to prosper in the 1990s and beyond.
"The party, the national movement and Scotland owe him a great debt and my condolences go to Edith and the family."
Deputy First Minister and family friend John Swinney said: "Gordon Wilson was a giant of the Scottish National Party. He was critical to the transformation of the SNP from the fringe to the mainstream of Scottish politics.
"His administrative, campaigning and political skills built the SNP into a nationwide political force. The strength of the SNP today is built on the courage and tenacity of fine people like Gordon Wilson."
Details of his funeral will be announced in the coming days, the SNP said.