Football Manager is a series of football management simulation games developed by Sports Interactive and published by Sega. The game began its life in 1992 as Championship Manager. However, following the break-up of their partnership with original publishers Eidos Interactive, Sports Interactive lost the naming rights and re-branded the game Football Manager with their new publishers Sega.
On 12 February 2004, after splitting from publishers Eidos Interactive, it was announced that Sports Interactive, developers of the Championship Manager game, had retained the rights to the source code but not the rights to the title Championship Manager, which were held onto by Eidos (who previously acquired the brand rights from Domark upon their merger in 1995). These developments led to a further announcement that future Sports Interactive football management games would be released under the famous Football Manager brand name. Whilst the Championship Manager series would go on, Eidos no longer had any source code, or, indeed a developer for Championship Manager.
Having been left without a publisher for its football management series, Sports Interactive teamed up with Sega and later, in April 2006, Sports Interactive was acquired completely by the publisher in a continuing trend of consolidation within the games industry.
The first game released under the newly acquired Football Manager brand was Football Manager 2005. Commonly known as "FM 2005", it competed directly with Championship Manager 5 from Eidos-funded Beautiful Game Studios.
Source: Wikipedia, "Football Manager", available under the CC-BY-SA License.