Former investment banker and Clongowes boy O'Callaghan (46, right) was a high-flying technology gazillionaire, building up Riverdeep and then Houghton Mifflin into one of the world's biggest online publishers before everything came unstock during the financial crisis.
The Cork man's near-billion euro fortune was vaporised when bondholders took control of the debt-laden company. He also had sizeable debts with Anglo.
However, O'Callaghan was nothing if not resilient and he set about rebuilding his fortune, through an e-learning business in China. Last year he sold his majority stake in Rise Global to Bain Capital for $140m. He also owns the Cliff House hotel.