Question: Who was the chief executive of the New York Stock Exchange during Black Monday, which was when stock markets around the world crashed?

Context paragraphs:
American Stock Exchange Building: The American Stock Exchange Building, formerly known as the New York Curb Exchange Building, is the former headquarters of the American Stock Exchange.  It is located on Trinity Place in the Financial District of Lower Manhattan, New York City.  Built in 1921 and enlarged in 1929-31, the building represents a link to the historical practices of stock trading outside the strictures of the New York Stock Exchange, which took place outside ("on the curb") prior to the construction of this building.  It was designated a National Historic Landmark in 1978.  The building presently stands vacant, the stock exchange having moved out after merging with the NYSE in 2008.

Buttonwood Agreement: The Buttonwood Agreement, which took place on May 17, 1792, started the New York Stock & Exchange Board now called the New York Stock Exchange.  This agreement was signed by 24 stockbrokers outside of 68 Wall Street New York under a buttonwood tree.  The organization drafted its constitution on March 8, 1817, and named itself the "New York Stock & Exchange Board".  In 1863, this name was shortened to its modern form, the "New York Stock Exchange".

2015–16 Chinese stock market turbulence: The Chinese stock market turbulence began with the popping of the stock market bubble on 12 June 2015 and ended in early February 2016.  A third of the value of A-shares on the Shanghai Stock Exchange was lost within one month of the event.  Major aftershocks occurred around 27 July and 24 August's "Black Monday".  By 8–9 July 2015, the Shanghai stock market had fallen 30 percent over three weeks as 1,400 companies, or more than half listed, filed for a trading halt in an attempt to prevent further losses.  Values of Chinese stock markets continued to drop despite efforts by the government to reduce the fall.  After three stable weeks the Shanghai index fell again on 24 August by 8.48 percent, marking the largest fall since 2007.

Consolidated Stock Exchange of New York: The Consolidated Stock Exchange of New York, also known as the "New York Consolidated Stock Exchange" or "Consolidated", was a stock exchange in New York City, New York in direct competition to the New York Stock Exchange (NYSE) from 1885-1926.  It was formed from the merger of other smaller exchanges, and was referred to in the industry and press as the "Little Board."  By its official formation in 1885, its membership of 2403 was considered the second largest membership of any exchange in the United States.

Black Monday (2011): In finance and investing, Black Monday 2011 refers to August 8, 2011, when US and global stock markets crashed following the Friday night credit rating downgrade by Standard and Poor's of the United States sovereign debt from AAA, or "risk free", to AA+.  It was the first time in history the United States was downgraded.  Moody's issued a report during morning trading which said their AAA rating of U.S. credit was in jeopardy, this after issuing a negative outlook in the previous week.

Black Monday (1987): In finance, Black Monday refers to Monday, October 19, 1987, when stock markets around the world crashed, shedding a huge value in a very short time.  The crash began in Hong Kong and spread west to Europe, hitting the United States after other markets had already declined by a significant margin.  The Dow Jones Industrial Average (DJIA) fell exactly 508 points to 1,738.74 (22.61%).  In Australia and New Zealand, the 1987 crash is also referred to as "Black Tuesday" because of the time zone difference.

Financial District, Manhattan: The Financial District, also known as FiDi, is a neighborhood located at the southern tip of the borough of Manhattan in New York City, which comprises the offices and headquarters of many of the city's major financial institutions, including the New York Stock Exchange and the Federal Reserve Bank of New York.  Anchored on Wall Street in the Financial District, New York City has been called both the most financially powerful city and the leading financial center of the world, and the New York Stock Exchange is the world's largest stock exchange by total market capitalization.  Several other major exchanges have or had headquarters in the Financial District, including the New York Mercantile Exchange, NASDAQ, the New York Board of Trade, and the former American Stock Exchange.

John J. Phelan Jr.: John Joseph Phelan Jr. (May 7, 1931 – August 4, 2012) was an American financier who served as president and later chairman and chief executive of the New York Stock Exchange, where he introduced computerized trading technology.  Phelan's leadership tenure at the NYSE included the 1987 stock market crash stock market crash, during which he declined to halt trading.  Phelan's calm and confident manner was widely praised.  After the crash, Phelan helped to implement trading curbs also known as "circuit breakers" to help prevent rapid stock selloffs in the future.

China Concepts Stock: China Concepts Stock is a set of stock of companies whose assets or earnings have significant activities in mainland China.  The People's Republic of China is undergoing major financial transformation, and many leading mainland-based companies have chosen to list themselves overseas to gain access to foreign investor capital.  Currently, there are China Concepts Stocks listed on several major stock exchanges around the globe, including the Hong Kong Stock Exchange (HKEx), Singapore Exchange (SGX), New York Stock Exchange (NYSE), NASDAQ, NYSE MKT (formerly known as the American Stock Exchange), London Stock Exchange (LSE), Euronext, and the Tokyo Stock Exchange (TSE).

Nasdaq, Inc.: Nasdaq, Inc. is an American multinational financial services corporation that owns and operates (and is listed on) the NASDAQ (formerly National Association of Securities Dealers Automated Quotations) stock market and eight European stock exchanges, namely Armenian Stock Exchange, Copenhagen Stock Exchange, Helsinki Stock Exchange, Iceland Stock Exchange, Riga Stock Exchange, Stockholm Stock Exchange, Tallinn Stock Exchange, and NASDAQ OMX Vilnius.  It is headquartered in New York City, and its president and chief executive officer is Adena Friedman.

Supporting paragraphs: John J. Phelan Jr. Black Monday (1987)
Answer: John Joseph Phelan Jr.