For more than nine years, Yeo Lian Sim stood guard over the Singapore Exchange (SGX) as its top risk and regulatory officer. She will step down at year-end, but filling her shoes is such a gargantuan task that two people will take over her portfolio.

Ms Yeo, 64, will retire when the new year arrives, but will retain a role as special adviser to SGX. Replacing her as chief regulatory officer will be current deputy chief regulatory officer Richard Teng. The chief risk officer hat will be donned by Agnes Koh, who is currently head of clearing risk. Like Ms Yeo, Mr Teng and Ms Koh held positions at the Monetary Authority of Singapore (MAS) before joining SGX.

"Lian Sim has built SGX's risk management and regulatory function into a well-respected, professional organisation with a worldwide reputation for expertise and execution," SGX chief executive Magnus Bocker said in a statement yesterday.

"She has been tireless in her pursuit of regulating a fair, orderly and transparent marketplace. We thank her for her invaluable contribution and send with her our very best wishes for a long and happy retirement."

Ms Yeo joined the exchange in July 2004 after an illustrious career at MAS and Temasek Holdings. She replaced Alan Shaw, who was one of the architects behind SGX's migration towards a disclosure-based regime.

Ms Yeo's legacy includes the creation of the sponsor-supervised regime for the Catalist board, as well as leading SGX to become one of the first exchanges in the world to meet post-global financial crisis international standards on clearing and risk management for exchanges.

Notably, she helped to steer the exchange through the global financial crisis. SGX's ability to quickly resolve and clear the debris from MF Global's 2011 collapse has drawn praise.

Some of her views have evolved over time. For the first several years of her time at SGX, she had resisted calls for circuit breakers in the market, arguing that the existing mechanisms were enough.

But as markets have become more complex, and with the possibility of high-frequency trading on the horizon, SGX is now laying some of the final pieces for a circuit-breaker system.

On her watch, SGX has also had to grapple with a number of corporate governance lapses among China-based companies that have tested the limits of the exchange's powers.

Ms Yeo sought to find a delicate balance as a regulator, saying in 2007 that "intervention with a heavy hand does not add to effective regulation".

But she has also been acutely aware of the importance of enforcement, through which regulators try to translate their ideals into reality.

"This is where regulators come in, to put flesh on the bones," she had said in 2007.