The Legionnaires Mercenaries are a group of elite mercenaries and an enemy faction encountered in Battlefield: Bad Company.
In Battlefield: Bad Company, they are dressed in all black with a mask over their faces and a helmet with goggles. They are hired by the MEC, the Russian Federation and Serdaristan. Sweetwater explains to Bad Company that they are the deadliest army in the world, and how each unit is paid in gold bars. If one stops at certain points in the game (mainly at the legionnaire symbols) Sweetwater will explain that they are somewhat of a myth and a legend known by the "spooks" in the intelligence community. He will go on to explain that a French Foreign Legion unit was on a patrol in Africa, when they stumbled on a hidden cache of Nazi gold. The future leader of the Legion conspires with those loyal to him and he kills his commanding officer and with the rest of his unit, take the gold, go rogue and become mercenaires. This explains why the soldiers seem so diverse, how they can afford all thier equipment, why they are so highly trained and why they only wish to be paid in gold.
The Legionnaires are the hardest enemies to beat in the entire game, as they are highly trained. They are most likely from Eastern Europe, as they have Russian accents, but some have Scottish accents, and a few have French accents, but they all speak English. They are presumably defeated after Preston Marlowe, shoots down the Legionnaire's Ka-52, but he does not die, so the Mercenaries may still be a viable faction to be featured in a future game of the Bad Company series.
The Legionnaire Mercenaries use new, high-tech weaponry, as well as vehicles provided from their hirers.