Mercenary

Mercenaries are people who fight in conflicts for the sake of direct profit provided by their employer. In most fiction, they exist to provide a group of people who have military force capacity, while not being associated with particular political and societal factions. This means that most mercenaries are used for protagonists and anti-heroes, as it's much easier to create a believable and unique character without restricting them to a set group of beliefs of a faction. Equally frequently, the mercenaries are shown in the dark light as well, being pragmatic villains who have little of interest in anything besides money, thus allowing them to be the bad guys by doing anything and everything evil for the sake of wealth.

This duality is frequently noted in Role Playing games, as in many a games the characters are hired as mercenaries to provide services for someone, starting from removal of Giant Space Hamsters from a cellar of a local noble, to poisoning the kings during a banquet, so his brother's cousin sister can usurp the throne. And since the parties can range from Chaotic Stupid to Stupid Evil to Stupid Good (even at the same time), this means that all characters can act towards common goal, without having to resort to fratricide, because they can't agree on an approach to the situation (as most players use their status as mercenary as an excuse to do things out of characters, because "Derp, Money").