Question: Which regional airline owned by Delta Air Lines was originally named Express Airlines?
Context: SkyWest Airlines is a North American airline owned by SkyWest, Inc. and headquartered in St. George, Utah, U.S..  According to the Airlines for America definitions, SkyWest is a North American major airline.  SkyWest however, operates on a regional airline level and is a member of the Regional Airline Association.  SkyWest Airlines flies to 238 cities, in 45 states; Washington, D.C., six Canadian provinces and five cities in Mexico.  The airline serves as a feeder airline, operating under contract with various major carriers.  It flies as SkyWest Airlines in a partnership with Alaska Airlines, as United Express on behalf of United Airlines, as American Eagle on behalf of American Airlines, and as Delta Connection on behalf of Delta Air Lines.  SkyWest also provides ground handling services for airports across the United States. Pinnacle Airlines Corporation was an American holding company headquartered in Memphis, Tennessee, and was the parent company of Pinnacle Airlines and Colgan Air until Colgan was closed down in 2012.  The company contracted its airlines to fly in the aircraft livery of other airlines such as Delta Air Lines and United Airlines.  The company filed for bankruptcy protection under Chapter 11 in 2012 and emerged from Chapter 11 in 2013 as a wholly owned subsidiary of Delta Air Lines.  The company's only surviving airline, Pinnacle, became Endeavor Air. United Airlines, Inc., commonly referred to as United, is a major U.S. airline headquartered in Chicago, Illinois.  It is the world's third-largest airline when measured by revenue, after American Airlines and Delta Air Lines.  United operates a large domestic and international route network, with an extensive presence in the Asia-Pacific region.  United is a founding member of Star Alliance, the world's largest airline alliance.  Regional service is operated by independent carriers under the brand name United Express.  Its main competitors are American Airlines, Delta Air Lines, and Southwest Airlines. As of September 2017, the Delta Air Lines mainline fleet comprises 852 aircraft in service, making it one of the largest airline fleets in the world.  Before merging with Northwest Airlines in 2009, Delta Air Lines operated an all-Boeing and McDonnell Douglas fleet; it incorporated Northwest's Airbus aircraft into its fleet following the merger and subsequently ordered further Airbus types.  Delta is known for its policy of generally buying older generation or used aircraft and for continuing to fly aircraft for 20–30 years, much longer than most other major airlines.  As such, it has one of the oldest fleets of any American airline, with an average fleet age of 17 years as of 2017.  Fellow U.S. legacy carriers American Airlines and United Airlines have much younger fleets; as of December 29, 2016, American had an average fleet age of 10.3 years, while United had an average fleet age of 14.1 years. Business Express Airlines (IATA: HQ) , often referred to as Business Express or BizEX, was an American regional airline founded as Atlantic Air in 1982.  In an effort to appeal to its predominantly business commuter clientele, the airline assumed the Business Express name in 1985.  In 1986 Pilgrim Airlines (Groton/New London), which itself had acquired NewAir (New Haven) about a year prior, was acquired by the airline.  This opened the valuable New York and Washington, D.C. markets.  Shortly thereafter, Business Express became one of Delta Air Lines's first Delta Connection carriers, along with Atlantic Southeast Airlines, Comair and SkyWest Airlines. Mesaba Aviation, Inc. (operating as Mesaba Airlines) was an American regional airline based in Eagan, Minnesota The airline was a wholly owned subsidiary of Pinnacle Airlines Corporation.  Its flights operated as Delta Connection for Delta Air Lines and US Airways Express for US Airways.  Previously, the airline operated as Northwest Airlink and Northwest Jetlink on behalf of Northwest Airlines which subsequently merged with Delta.  Mesaba Airlines effectively ceased operations on January 4, 2012, when all aircraft and personnel were transitioned to the Pinnacle Airlines operating certificate.  Mesaba's operating certificate was surrendered on July 31, 2012. Pierre Regional Airport (IATA: PIR, ICAO: KPIR, FAA LID: PIR) is a city owned, public airport three miles east of Pierre, in Hughes County, South Dakota, United States.  The airport was served by two airlines until January 31, 2012 when Delta Air Lines regional affiliate Delta Connection ceased all service.  Great Lakes Airlines now flies both east and west via interline agreements with Delta Air Lines, Frontier Airlines and United Airlines. Delta TechOps is the maintenance, repair and overhaul (MRO) division of Delta Air Lines, and is headquartered at Hartsfield-Jackson International Airport (ATL) in Atlanta, Georgia.  With more than 9,600 Technical Operations employees and 51 maintenance stations worldwide, Delta TechOps is a full-service maintenance provider for the more than 750 aircraft that make up the Delta Air Lines fleet.  In addition to maintaining the Delta Air Lines fleet, Delta TechOps also provides MRO solutions and support to more than 150 third-party operators around the world, making it the largest airline MRO provider in North America and the third largest worldwide. Endeavor Air is an American regional airline that operates as Delta Connection for Delta Air Lines.  The airline was founded as Express Airlines I in 1985 and changed names to Pinnacle Airlines in 2002.  In 2012, Pinnacle's parent company filed for chapter 11 reorganization, then emerged as a wholly owned subsidiary of Delta Air Lines.  The name of the airline was changed to Endeavor Air on August 1, 2013. Delta Connection is a regional airline brand name for Delta Air Lines, under which a number of individually owned regional airlines operate short- and medium-haul routes.  Delta's lone wholly owned regional airline, Endeavor Air, also resides under the Delta Connection banner.  Mainline carriers often use regional airlines to operate services in order to increase frequency, serve routes that would not sustain larger aircraft, or for other competitive reasons.
Answer: Endeavor Air