BELFAST (Reuters) - Ireland's former richest man, Sean Quinn, was declared bankrupt on Friday after having bet the family fortune on the shares of Ireland's most notoriously profligate bank just before it collapsed. Quinn, 64, developed a quarrying operation in the northern county of Fermanagh in 1973 into a global organisation with insurance and property interests. He amassed a fortune of 4 billion euros ($5.4 billion), before investing massively in the now failed Anglo Irish Bank, one of the biggest casualties of Ireland's property bubble. "It is with great sadness and regret that I have applied for voluntary bankruptcy in the High Court in Belfast today," Quinn said in a statement.