Jack Alan Markell (born November 26, 1960) is an American politician and diplomat. He had served the United States ambassador both to Italy and to San Marino. He had served as the United States ambassador to the Organisation for Economic Co-operation and Development. As a member of the Democratic Party, He previously served as the 73rd governor of Delaware from 2009 to 2017.

Markell served three terms as the state treasurer of Delaware from 1999 to 2009. After term-limited Governor Ruth Ann Minner was prevented from running for reelection, Markell announced his intention to run. He defeated lieutenant governor of Delaware John Carney with 51% of the vote in the Democratic primary, and defeated the Republican nominee, former Delaware Superior Court judge Bill Lee, with 67% of the vote in the 2008 general election, becoming Delaware's first Jewish governor. Markell won reelection in 2012 by a margin of over 40%.

On May 12, 2023, President Joe Biden nominated Markell to serve as the United States ambassador to Italy and San Marino, serving until the end of the administration. He was confirmed by the Senate on July 27, 2023.

Markell was born and raised in Newark, Delaware, the son of Elaine "Leni", a social worker, and William Markell, who taught accounting at the University of Delaware. He graduated from Newark High School. As a child, he attended Camp Galil, a summer camp in the Labor Zionist youth movement, Habonim Dror. He graduated from Brown University earning his Bachelor of Arts in economics and development studies, and went on to the University of Chicago Booth School of Business, earning his Master of Business Administration (MBA).

Markell began his business career in 1982, working as a banker at First Chicago Corporation. He then became a consultant at McKinsey & Company in 1986. Markell joined Fleet Call – later known as Nextel Communications (a name that Markell coined) – where he served as the senior vice president for corporate development from 1989 to 1995. Becoming the company's 13th employee, Markell joined Nextel when the company was in a nascent stage; helping lead Nextel to nationwide success during the wireless telecommunications revolution of the 1990s. After leaving Nextel, Markell worked as a senior manager at Comcast Corporation from 1996 to 1998.

Markell was first elected state treasurer of Delaware in 1998, unseating four-term Republican incumbent Janet Rzewnicki, and was re-elected in 2002 and 2006.

As treasurer, Markell led the development of several educational efforts in personal financial management, known collectively as "the Financial Literacy initiatives". He created the "Delaware Money School", which offers free classes to Delaware residents on topics such as saving for college and retirement planning. He also started the "Delaware Bank at School Program" which takes banks and financial education to schools. He partnered with the University of Delaware, Center for Economic Education and Entrepreneurship, as well as several Delaware banks, to teach young people the basics of money and savings.

In 2001, Governor Ruth Ann Minner chose Markell to chair the information services task force, which developed and implemented recommendations to modify the state's management of information technology. In 2002, he led an effort to streamline and coordinate the procurement of goods and services while using state-of-the-art purchasing techniques. He also led the "Health Rewards" initiative, which offers Delaware state government employees comprehensive physical assessments, detailed statistics about how their health compares with their peers across the country, and recommendations about how they can improve their health.