Gren, one of Wales' best-known and long-serving newspaper cartoonists, has died aged 72.
Gren - real name Grenfell Jones - drew daily cartoons for the South Wales Echo for more than 35 years.
His cartoons depicted south Wales valleys life, centred on the fictional village of Aberflyarff.
First Minister Rhodri Morgan paid tribute to the award-winning cartoonist, saying Wales was "much the sadder for his passing".
"Gren's cartoons were always funny, and that's the number one job of a cartoonist - to put something that's funny into a well-drawn cartoon and Gren could do that like nobody else," Mr Morgan said.
"We're all much the sadder for his passing. there's never been another chronicler of the post-industrial age arriving and the industrial age declining like Gren.
"I don't envy the task of the South Wales Echo to find a cartoonist who can fill those giant shoes."
And the first minister said he never minded appearing in a Gren cartoon.
"It is a great honour - to be lampooned by Gren means that you have arrived as a politician."
The Welsh Rugby Union (WRU) also paid tribute to the cartoonist who it said had helped to immortalise "the great Welsh players of the seventies".
"Welsh rugby has lost a great friend. For almost 40 years he lit up the lives of Welsh people around the world with his fantastic grip on Welsh life and humour. Who can ever forget the village of Aberflyarff, Bromide Lil and Attila Groinstomper," said WRU group chief executive Roger Lewis.
Gren was voted best provincial cartoonist in Britain four times during the 1980s and was made an MBE for services to newspapers in 1989.
Gren, who lived in the Llandaff area of Cardiff, died at the city's University Hospital of Wales on Thursday morning.
Born in Hengoed, Rhymney Valley, he produced daily cartoons for the Echo at its Cardiff base for 30 years before retiring on his 65th birthday in 1999.
But he continued to produce cartoons for the evening paper from home as well as producing his annual rugby calendar and over 24 books.
Gren's humour concentrated on traditional valleys life in south Wales, with rugby, tightly-packed terraced streets and Nigel and Neville the message-bearing sheep, frequently recurring images.
Many of his original drawings have been sold at auction to raise thousands of pounds for charity and he was awarded an MBE for his services to newspapers in 1989.
Speaking at the time of his 1999 retirement, he said his themes, which won him a world-wide audience, had remained consistent.
'Crazy on rugby'
"When I started out I enjoyed the same things as I'm drawing now," he said.
"Wales, rugby, local politicians, anything we in this part of the world are able to relate to - I aim to reflect our life and it goes down well with the readers.
"I'm not trying to prove any points. I try not to get into the political area as that isn't my audience."
Fellow cartoonist Bill Tidy said he was "a great admirer of Gren".
He said: "To me he was a Max Boyce on paper and a Harry Secombe in humour.
"He raised a large amount of money for charity, he was crazy on rugby and was the only Welshman I'd ever met who sang out of tune deliberately.
"He had his finger on the pulse of Wales."
A repeat tribute showing of the On Show documentary Gren: How To Be A Welshman, first shown in 2004, will be screened on BBC2 Wales/2W on 9 January at 1900 GMT.