He was the leader of one of the largest mass defections in private banking history, with more than 100 staff following him from RBS Coutts Bank Ltd. in the thick of the global credit crisis to create a financial phenomenon in Singapore at a little-known Swiss bank. Hanspeter Brunner, together with former deputy Raj Sriram and chief operating officer Gary Tucker, were the kernel of a plan by BSI SA, founded in 1873 in Lugano, to build up a $10 billion wealth-management business serving the burgeoning ranks of Asia’s millionaires.