From Wikipedia: The Mercenary series consists of three main games and a number of add-on datasets. While each game is self-contained, they make occasional references to other games in the series and are connected in terms of their freeform, open-ended gameplay, visual appearance and general ambience.
Within each game the player must explore a world rendered in realtime 3D graphics, completing a number of non-linear tasks in order to achieve a single main objective. The title of the series derives from the player's role in carrying out tasks as a "hired gun". In Mercenary the player crash lands into an ongoing conflict and is able to play the warring factions off against one another to the player's own advantage. In Damocles the player is encouraged to bargain the fate of a whole world for financial reward. However, in The Dion Crisis the player has a less selfish agenda, and must gain the support of voters against the plotting of a sinister businessman.