Take the time machine back to 25 years ago, and financial markets are experiencing lingering effects of the 1987 stock-market crash. In response to the unexpected meltdown, Federal Reserve Chairman Alan Greenspan adds liquidity to the market by buying government securities.  Fast forward to 2014, and the markets don't look drastically different: Ben Bernanke steps down as the Fed chief with quantitative easing—a bond-purchasing policy established after the 2008 financial crisis—still in place.  History may repeat itself in financial markets, but if there's one thing unpredictable about Wall Street, it's the people in it.  (Read more: Finance kings: The bailouts, bonds and bubbles)  As CNBC celebrates its 25th anniversary, we're looking to find the top 25 most influential leaders of the past 25 years.  Like any other sectors, Wall Street has had its fair share of good, bad and ugly leaders. But their influence reaches far beyond the Street, says John Longo, a professor at Rutgers Business School.  Jamie Dimon is currently the top Wall Streeter in the CNBC 25 voting. The often blunt CEO of JPMorgan Chase rose up the ranks of Wall Street and, after being ousted from Citigroup by former CEO Sandy Weill, later went on to the top job at JPMorgan and is credited with leading the bank through the financial crisis relatively unscathed compared to other banks.  Of course, it hasn't been all smooth sailing: Dimon has navigated JPMorgan through the "London whale" trading debacle, a lawsuit over mortgage-backed securities and a lawsuit over the bank's ties with Bernie Madoff.  But, the head of America's biggest bank is still regarded as one of the best executives today, Longo said.  "Whether it's due to coincidence or due to his skill, there's been a tale of two cities between Citi and JP Morgan," he said. Dimon "was forced out of Citi, and Citi was ultimately near bankruptcy while JP Morgan thrived."  (Read more: Jamie Dimon vs. Sandy Weill: Who is more influential?)  Weill is also among the bankers in contention for CNBC's most influential of the past 25 years, along with Goldman Sachs CEO Lloyd Blankfein, former Goldman CEO and former Treasury Secretary Hank Paulson, and former Bank of America CEO Hugh McColl.
Are big bank leaders like Jamie Dimon the most influential on Wall Street—or activist investors like Carl Icahn?