Former Welsh first minster Rhodri Morgan collapsed and died while cycling in lanes near Cardiff.
The 77-year-old politician was “both the father of devolution and the father of the nations”, former Welsh secretary Lord Hain said.
Political parties in Wales suspended campaigning for the General Election on Thursday, following news of Mr Morgan’s death.
A minute’s silence was held at the Senedd in Cardiff Bay, where a book of condolence for Mr Morgan has been opened.
Tributes have been paid to Mr Morgan, who led Wales as first minister for almost 10 years from 2000, from across the political spectrum
In a statement, South Wales Police said officers were called to a lane near Cwrt Yr Ala Road, Wenvoe, shortly after 5pm on Wednesday to reports a man “had been taken ill”.
“Police and paramedics attended. Sadly, the man, former First Minister Rhodri Morgan, was pronounced deceased at the scene,” a force spokeswoman said. “Next of kin have and HM Coroner have been informed.”
It is understood that Mr Morgan had been cycling at the time.
A spokeswoman for the Welsh Ambulance Service said paramedics were called to a “medical emergency” at 5.06pm on Wednesday.
“We sent an emergency ambulance to the scene, where the crew were supported by our Hazardous Area Response Team and a doctor from the Emergency Medical Retrieval and Transfer Service,” she added.
Welsh Labour, Welsh Conservatives, Plaid Cymru, the Welsh Liberal Democrats and Ukip Wales suspended campaigning on Thursday as a mark of respect.
Mr Morgan’s wife Julie is Assembly Member for Cardiff North.
The politician made a name for himself on the Welsh political scene in 1987 after being elected as MP for Cardiff West, working as shadow environment spokesman and chairing the House of Commons public administration select committee before assuming office in the Assembly in 1999.
After standing down as an MP in 2001, Mr Morgan retained his Assembly seat following the 2003 and 2007 elections.
In September 2009, on his 70th birthday, Mr Morgan announced he would be relinquishing his post as first minister, with Bridgend AM Mr Jones succeeding him.
Around 12 months later, Mr Morgan announced he would be retiring from politics altogether.
Paying tribute, Mr Jones said he was “very shocked, desperately sad”, adding that his thoughts were with Mrs Morgan and the family.
Mr Jones described Mr Morgan as “someone who was strong but courteous and that’s a lesson for us all”.
Lord Hain added that Mr Jones was “Welsh through and through and a repository of fascinating facts on everything under the sun”.
Following his retirement from politics in April 2011, Mr Morgan said he planned to catch up on his gardening and wood-carving, as well as finally getting round to learning the piano.
Six months later, he was appointed chancellor of Swansea University.
Professor Richard B Davies, vice-chancellor of the university, said his thoughts were with Mrs Morgan, their children and grandchildren and his brother Prys.
“He had an infectious enthusiasm for life and education,” Prof Davies added.
Books of condolence have been opened by the National Assembly for Wales at the Senedd in Cardiff Bay and the Assembly’s office in Colwyn Bay.
Assembly members, staff and visitors observed a minute’s silence at 12.30pm.