Space Shuttle Endeavour (Orbiter Vehicle Designation: OV-105) is a retired orbiter from NASA's Space Shuttle program and the fifth and final operational shuttle built. It embarked on its first mission, STS-49, in May 1992 and its 25th and final mission, STS-134, in May 2011. STS-134 was expected to be the final mission of the Space Shuttle program, but with the authorization of STS-135, Atlantis became the last shuttle to fly.
The United States Congress authorized the construction of Endeavour in 1987 to replace Challenger, which was lost in 1986.
Structural spares built during the construction of Discovery and Atlantis were used in its assembly. NASA chose to build Endeavour from spares rather than refitting Enterprise or accepting a Rockwell International proposal to build two shuttles for the price of one on cost grounds. (wikipedia)