Final answer:
J.P. Morgan acted as the de facto lender of last resort during the 1907 panic, providing critical funding to stabilize the financial system.
Step-by-step explanation:
During the 1907 panic, which is also known as the Bankers' Panic, J.P. Morgan served as a de facto lender of last resort. At the time, banks ceased lending due to fears of not being repaid, which jeopardized the stability of the U.S. economy. In response, J.P. Morgan stepped forward and provided the necessary funds to prevent banks from collapsing, thereby restoring investor confidence in the financial system.