Hugh Adam, the one-time chairman and managing director of Rangers Development, passed away on Saturday after suffering from heart failure.
He was 87 and had recently celebrated his 60th wedding anniversary with wife Jean, 85.
Mr Adam, of Burnbank, South Lanarkshire, brought £18 million of new investment to the club.
But his 30-year association with Rangers ended in 2002, when he sold his 59,000 club shares, claiming that under Sir David Murray's ownership they would become "worthless".
Early last year, after the club entered administration, he claimed that, contrary to SPL Rules, Rangers made undisclosed payments and deliberately excluded them from players' contracts.
The SPL launched an investigation into Rangers' payments schemes last March following Mr Adam's allegations, a process which is expected to accelerate in the weeks ahead.
A Rangers spokesman said: "We are sorry to learn of the death of Mr Adam. Our thoughts are with the family at this sad time."