Today the public will see for themselves the massive mural by Mr Gray which adorns one of the street level walls of Hillhead Subway station.
The work of art, which is 7ft tall and more than 40ft wide and depicts a panoramic view of Hillhead, was officially unveiled by the 77-year-old artist and author.
It marks the completion of work at Hillhead Subway – the first 15 city stations to undergo a facelift.
Modernisation work at Hillhead has involved installing two new escalators, moving the ticket office and creating retail space, new information and signs for passengers, hearing loops for the hard of hearing, tactile maps and paving for vision impaired passengers, colour contrast flooring and brighter, more welcoming energy-efficient lighting.
The mural, which took 14 months to complete, combines elements of "realism, fantasy and science fiction".
Its theme, which was drawn and designed by Mr Gray, before being transferred to hard-wearing tiles for the Hillhead station, is "all kinds of folk".
Creator of spectacular murals at The Ubiquitous Chip restaurant and the Oran Mor venue in Glasgow, Mr Gray said: "The station is in the centre of Hillhead, which I know well.
"I have lived and worked in the district since 1969, and I knew I would enjoy depicting it, and those who use the Subway, in a symbolic and humorous way."
The artist was approached to create the mural by SPT, because of his strong links with Glasgow's West End.
Vice-chairman of SPT, David Fagan, said: "Hillhead is the first of our stations to be modernised, and we wanted to take this opportunity to make a bold statement about the importance we place on art in the Subway."