A talented pianist, Donald was regarded as the musical brains of the group, which also included the late Steve Robertson and William "Buff" Hardie.
The comedy stars, who all came from around Aberdeenshire, shot to fame after making their debut in 1969.
Many of their sketches and songs were performed in the north-east Doric dialect and were based on their brand of local humour.
The trio were given the Freedom of the City of Aberdeen in 2008.
Paying tribute to his friend, Hardie said he had brought a touch of class to the group's shows.
He said: "George was a vital part of the show's chemistry. More than that, he was a very good friend for 55 years.
"He was ill for many years, as long ago as the time we were given the Freedom of the City of Aberdeen.
"But he carried on performing for years afterwards. That took courage."
He added: "He was a great performer - as a pianist and accompanist - I don't know anyone else who could have done what he did. He was incredibly versatile.
"We came to be known as couthy and classy: it was George who made us classy."
The north-east entertainers had a career which took them around the world, and were made MBEs for services to entertainment in Scotland in 1995.
Aberdeen City Council said its flag would fly at half mast as a mark of respect to Donald.
Lord Provost George Adam said: "George Donald was an exceptional musician, a brilliant entertainer and a true gentleman.
"His talents as a pianist inspired countless pupils and performers, and everyone lucky enough to see him on stage with Scotland the What? went home with broad smiles on their faces.
"Our thoughts are with his family and friends."
Robertson died in 2011.
Obituaries: Page 16