Stanley Fischer, the number two official at the Federal Reserve, unexpectedly submitted his resignation Wednesday, citing "personal reasons."

The vice chairman's resignation, effective Oct. 13, will allow President Trump to replace him at the central bank three-quarters of a year ahead of schedule. Fischer likely would have been an obstacle to Trump's ambitions for cutting back regulations on banks, as he described the effort to loosen rules on big banks as "very, very dangerous" last month.

Already, Trump faced a major task in choosing the next chairman of the Fed before February and replacing most of the central bank's Board of Governors. One Fed watcher called it the biggest overhaul of the Fed's leadership since 1936.

President Obama had appointed Fischer to the Fed in 2014. Fischer, a 73 year-old who was born in what is today Zambia, had previously served as the governor of Israel's central bank. Before that, he worked at Citigroup and had a noted academic career as an economist, training several economists who would go on to helm the world's most important central banks.

Fischer didn't elaborate on the personal reasons that led to his abrupt resignation. In the letter he sent to Trump, he said that it was a "great privilege" to serve at the Fed and wrote that the economy has strengthened while the financial system has become "stronger and more resilient."

"Stan's keen insights, grounded in a lifetime of exemplary scholarship and public service, contributed invaluably to our monetary policy deliberations," Fed Chairwoman Janet Yellen said in a statement. "He represented the Board internationally with distinction and led our efforts to foster financial stability."