William Brodsky, who transformed CBOE Holdings from a member-owned exchange into a for-profit company best known as the home of Wall Street’s favourite fear index, has unexpectedly announced he will step down as chief executive in May.

Brodsky, 68, will be succeeded by president and chief operating officer Edward Tilly, 49, CBOE said. Brodsky, who has run the operator of the oldest and largest US options exchange since 1997, is expected to become executive chairman.