J. P. Morgan and his friends.
JP Morgan was in fact who did that pre-Fed as I suspect you know.
His last time of backstopping the banking system was the 1907 Panic. He then let Teddy Roosevelt and Congress know that the U.S. economy had grown too big for him and his ad hoc rescue party of NYC bankers to be able to do this again. Morgan was a prime force pushing for the creation of the National Monetary Commission and advocated a central bank modeled after the ones in Europe. This eventually led to Congress creating the Fed.