Which investment bank's bankruptcy became a defining event of the 2008 financial crisis?

Lehman Brothers’ bankruptcy became a defining event of the 2008 financial crisis.

Lehman Brothers filed for Chapter 11 bankruptcy protection on September 15, 2008, after suffering enormous losses tied to mortgages and real estate. With about $639 billion in assets, it was the largest bankruptcy filing in U.S. history at that time.

The failure intensified fear throughout global credit markets. Banks and investors became less willing to lend because they could not easily judge the exposure of other institutions to mortgage-related securities. The resulting loss of confidence contributed to a severe liquidity crisis and further stock-market declines.

Lehman was not the first major firm in trouble. Bear Stearns had been rescued in March 2008, and the government had placed Fannie Mae and Freddie Mac into conservatorship shortly before Lehman failed. The U.S. government later supported the rescue of American International Group, while Merrill Lynch was acquired by Bank of America.