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, Hamilton in Lanarkshire, brought £18 million of new investment to the club through the Rangers Pools, around £70m in today's money.
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".
As Rangers' debts mounted under the excesses of the Dick Advocaat era, Adam described bankruptcy as "the logical conclusion" for a team in financial free-fall.
Early last year, after the club entered administration, he claimed that, contrary to Scottish Premier League 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 ongoing and expected to accelerate in the weeks ahead.
SPL lawyers Harper Macleod are looking into dealings back to the league's formation in 1998.
A spokesman for Rangers said: "We are sorry to learn of the death of Mr Adam. Our thoughts are with the family."