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.

Its corporate headquarters are on the property of Minneapolis-Saint Paul International Airport, and it has hubs at Detroit Metropolitan Airport, Minneapolis-Saint Paul International Airport, and New York's LaGuardia Airport and John F. Kennedy International Airport. Until the restructuring, Endeavor also operated hubs at Delta's Hartsfield-Jackson Atlanta International Airport and Memphis International Airport hubs.

In February 1985, the airline was established as Express Airlines I, offering regional airline service to major airlines. The airline's founder, Michael J. Brady, had planned to create several regional airlines under parent company Phoenix Airline Services, Inc, hence the roman numeral "I" in the name.

Express I began its first code sharing agreement, in May 1985, with Republic Airlines. Republic was the dominant carrier in Memphis but, in keeping with the hub-and-spoke concept, wanted to add more smaller cities and free up its larger DC-9 jets to serve longer stage-length routes. Express I accomplished this by adding service, operating as Republic Express, to 3 cities using BAe Jetstream 31 aircraft. Within six months, Express Airlines I was operating in ten markets using nine Jetstream 31s and two Saab 340 aircraft.

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