Iain Russell, 76, spent 40 years in the Merchant Navy, rising to become a chief engineer. He and his wife Irene lived in Shotts, North Lanarkshire, but also spent time in her home town of Manchester.
She died two years ago and Mr Russell's health deteriorated before he suffered a brain haemorrhage and died in October last year.
He has shocked long-standing friends and neighbours after it emerged he had secretly built up a £1,231,180.76 fortune held in bank accounts and stocks.
He left £62,000 to friends and family but ordered the rest of his money be shared by four charities, which stand to receive about £290,000 each before tax.
Diabetes Scotland, MacKenzie Fund for Heart Cardiology, the Guild of Benevolence of the Institute of Marine Engineering and the Royal National Institute for the Blind will all receive windfalls.