X-Force is an X-Men spin-off originally developed by Rob Liefeld. The first X-Force team consisted of most of the original New Mutants cast, with Cable taking over as group leader and transforming the group into a more aggressive, militaristic version of the X-Men.
Following Liefeld's departure the title floundered for a while. In 2001 a new cast was introduced, who were media stars of a team that was now corporate sponsored. This group eventually became X-Statix.
From 2007, X-Force has been the name of several X-Men sub-teams with a black-ops/strike-force theme.