Eugene Murtagh (76) chairs Cavan insulated panel and building materials manufacturer Kingspan, which he founded, and owns a stake of about 16pc in the firm, worth approximately €1.08bn.
The firm's sales are approaching €4bn and profits nearing €500m, though the share price has risen and fallen by about 15pc either way over the year. It employs 13,000 people around the world.
Eugene, the father of Tesla-driving CEO Gene, sold about €40m worth of his holding in the company in June. The Murtaghs own the Hempel Hotel in London and another in Amsterdam. Faxitron, a US digital specimen radiography firm that Murtagh Snr owned through a number of Irish investment vehicles, sold to Nasdaq-listed women's health firm Hologic for about €75m last July. There is about €45m of assets in other companies. There is also an investment in a US probiotic supplements maker.