The Lanark author was hailed by his publisher Canongate, who announced his death, for his “phenomenal body of work”.
Gray produced novels, short stories, poems and visual art, as well as plays for television, radio and the stage, throughout a career that can be traced back to the 1950s.
The Glasgow School of Art graduate, who passed away the day after his 85th birthday, was described by his family as “unique and irreplaceable”.
The celebrated author was honoured with a lifetime achievement award for his contribution to Scottish literature at the Saltire Society literary awards last month.
His family said he had passed away in the Queen Elizabeth University Hospital in Glasgow after a “short illness”, adding that he had insisted his body be donated to medical science and did not want a funeral.
The family added: “Alasdair was an extraordinary person; very talented and, even more importantly, very humane.”
Gray was born in Glasgow in 1934 and studied and later taught at the city’s art school.
Lanark, which was finally published in 1981, won him the Saltire Scottish Book of the Year title.
Gray, who won the same award in 2011 with his autobiographical book A Life In Pictures, also wrote plays for television, radio and the stage and has been a prolific painter. Some of his best-known work in Glasgow was created for the Hillhead underground and the Oran Mor arts centre.
Gray was honoured with a major exhibition of around 100 works at Glasgow’s Kelvingrove Art Gallery and Museum in 2014 to mark his 80th birthday.
However, he was unable to walk since seriously injuring himself in a fall in 2015 – weeks before an adaptation of Lanark was due to be staged at the Edinburgh International Festival.
His public murals are visible across Glasgow, with further examples of his work on display in galleries from the V&A to the Scottish National Gallery of Modern Art.
'A bright star'
Nick Barley, director of the Edinburgh International Book Festival, said: "Scotland has been blessed with a host of great writers over the past 50 years, but if history remembers only one, it will likely be Alasdair Gray.
"He was a bright star in a luminous constellation of northern lights; a game-changer whose boundlessly innovative, cross-disciplinary thinking paved the way for so many others to succeed.
"We can thank Alasdair not only for his own great work, but for his role in creating the conditions for a literary renaissance that has, in so many different ways, changed most people’s understanding about what it means to be Scottish today."
In a tribute posted on Twitter, First Minister Nicola Sturgeon said: “Such sad news. Alasdair Gray was one of Scotland’s literary giants and a decent, principled human being. He’ll be remembered best for the masterpiece that is Lanark, but everything he wrote reflected his brilliance.”
Francis Bickmore, Gray’s editor at Canongate, said: “It seems hard to believe that Alasdair was mortal and might ever leave us. At least through Gray’s phenomenal body of work, he leaves a legacy that will outlive us all.”
Sarah Mason, programme director at the Saltire Society, said: “His inspiration has reached generations and will continue to do so for many more to come.”
In a tribute posted on Twitter, author Irvine Welsh said: “Alasdair Gray was a unique talent. In Lanark, and 1982 Janine especially, he wrote two of the greatest Scottish novels and influenced a creative generation.”
Crime writer Ian Rankin posted: “Remembering Alasdair Gray by reading his words and looking at his art. He’s gone; they remain.”