Former first minister Rhodri Morgan has died, aged 77.
Wales has “lost a father figure”, his successor Carwyn Jones said.
Mr Morgan was elected as an MP in 1987 and became an AM when the assembly was created in 1999.
He took the helm of the assembly nine months later, replacing Alun Michael who had stood down. He is widely credited with having brought stability to the fledgling institution after a turbulent start.
Mr Morgan served as first minister for nine years, from 2000 to 2009, before Mr Jones took over as first minister and Welsh Labour leader.
The former AM for Cardiff West is survived by his wife, Julie, two daughters and a son.
Following the news, a Welsh Labour spokeswoman said the party will suspend general election campaigning on Thursday.
Mr Jones said: “Wales hasn’t just lost a great politician, we’ve lost a real father figure.”
He said Mr Morgan was “funny, clever, engaging on almost any topic”.
“I owe him a great deal, just as we all do in Wales,” Mr Jones said.
“He did so much to fight for, and then establish devolution in the hearts and minds of the public in our country.”
Jeremy Corbyn, UK Labour leader, said: “We’ve lost a good friend, a great man and, above all, a giant of the Welsh labour movement.”
“I saw Rhodri just last month, campaigning in Cardiff North with Carwyn Jones,” he said.
“Rhodri was an incredibly effective first minister for Wales. He stood up for Wales, its people’s future and its public services.”
Tony Blair, who was Labour prime minister when Mr Morgan was installed, said he “was an outstanding servant of Wales, the United Kingdom and the Labour Party”.
“He was great company, a fund of marvellous stories and a shrewd and immensely capable politician”, Mr Blair said, adding that the former first minister led the assembly with “with enormous skill and dedication”.
Ex-Labour Welsh Secretary Lord Hain said: “As first minister Rhodri was both the father of devolution and the father of the nation.
“He did more than anyone to bed down and ensure the new Welsh Assembly gained widespread legitimacy.”
Calling him a “unique populist intellectual”, Lord Hain said Mr Morgan was a “towering figure in every sense whom we will all miss”.
Alun Michael, now Police and Crime Commissioner for South Wales, said he was “shocked by the sad news of Rhodri Morgan’s death”.
He said his commitment to Wales was “always absolute”.
“He was the most popular politician of his generation and the absolute master of the one-liner,” he added.
“While we had our disagreements, for instance over the Cardiff Bay Barrage, Rhodri was always a vigorous and colourful debater, but not personal.”
Rhodri Morgan’s time as first minister included two coalitions.
In the first, with the Liberal Democrats between 2000 and 2003, Mike German served as deputy first minister.
Lord German called the former Welsh Labour leader a “strong opponent but a great friend”.
“Wales has lost a great politician and stalwart tonight,” he said.
Plaid Cymru’s Ieuan Wyn Jones, who was deputy first minister to Mr Morgan under the One Wales coalition, said: “He was very easy to work with, and he was very likeable, extremely loyal and highly knowledgeable.
“It wasn’t easy for him to deliver the coalition in sections of his party, but Rhodri stood firm and we agreed a very progressive programme of government.”
Welsh Secretary Alun Cairns, himself a former AM who sparred with Mr Morgan in the Senedd chamber, said he was “a significant politician” and “great servant to Wales”.
Plaid Cymru leader Leanne Wood said the former first minister “was much respected across the political spectrum and led Wales with distinction during a crucial period in Welsh history”.
Expressing her deepest sympathy on behalf of the members of the assembly and its staff, the institution’s presiding officer Elin Jones said: “As First Minister of Wales, Rhodri’s contribution in helping build our nation and its young democracy was immeasurable.
“Rhodri’s ability to communicate with, and to understand, the diverse communities of Wales ultimately won hearts and minds, and was critical in giving the people of Wales the confidence to strengthen and develop the National Assembly.”
‘He spoke like no other politician’
By Tomos Livingstone, BBC Wales political correspondent
Rhodri Morgan stabilised Welsh devolution after its rocky first year, and spent nine years as first minister in his own idiosyncratic style.
At a time when sound bites were the norm, he spoke like no other politician – his response to being asked whether he wanted to lead the yet-to-be-created assembly was “do one-legged ducks swim in a circle?”
In office he pursued a strategy of differentiating his administration from Tony Blair’s New Labour government, using the new devolved powers to opt-out from Blairite reforms to health and education.