Lehman Brothers was a global investment bank founded in 1850 that provided investment banking, trading, and financial advisory services. Once a major Wall Street institution, it became heavily exposed to subprime mortgage securities in the mid-2000s. On September 15, 2008, Lehman Brothers filed for bankruptcy with over $600 billion in liabilities, triggering a severe escalation of the global financial crisis and reshaping the regulatory landscape for financial institutions.