Xbox 360 was the first Xbox console to offer backward compatibility with selected original Xbox games.
Microsoft added backward compatibility to Xbox 360 through software emulation and system updates. The feature allowed certain original Xbox games to run on the newer console, although compatibility was limited to an official list rather than covering the entire library.
The original Xbox used a different hardware architecture from Xbox 360, so supporting older games required Microsoft to reproduce aspects of the earlier system through software and game-specific configuration. Some titles also needed compatibility updates delivered through Xbox Live.
Backward compatibility later returned in a much broader program for Xbox One, which supported selected original Xbox and Xbox 360 games. Xbox Series X|S continued that compatibility work, but those later systems were not the first Xbox consoles to introduce the idea.