MTA chairman Jay Walder abruptly announced his resignation Thursday, letting Gov. Andrew Cuomo know he will need to be replaced after Oct. 21.

Walder accepted a position as CEO?of the MTR Corporation in Hong Kong, which operates rail services in Asia and Europe. He joined the MTA in 2009 and oversaw the city’s transit system through both bad and good times. He implemented service cuts and fare hikes, but he was also the driving force behind Select Bus Service and the installation of countdown clocks.

“The job wasn’t what he expected when he came here,” said Bill Henderson, head of the MTA’s Permanent Citizens Advisory Committee. “He thought he would be building a system rather than cutting things.”