Marauders are a new type of enemy NPC that was added to Fortnite in Chapter 2 of Season 3. Marauders will roam the map in gangs of five, armed with a variety of weapons, and they're actually pretty difficult to deal with if you are alone. The Mauraders have a pretty aggressive default AI and, for now, can easily take you from a good distance. They also won't drop aggro if you go into hiding, although it is not yet known whether this works as intended.
Marauders arrive on the map from drop pods that will spawn early in the round. If you pay attention to the sky in the first few minutes of a match, you'll notice thunder, with a circular pattern of lightning, appearing in two or three places on the map. It's the arrival of the Marauders, and their pods will fall to the ground, opening and unleashing them across the map. There is no way we know of to predict where they will end up, it will be random from match to match.
If you get close to the Marauders in the game, you'll also hear some strange music, which is a nice warning that a death squad is about to knock you down. Marauders will happily roam the entire map in a random pattern they fall from and will always try to stay ahead of the storm, so unless they are dealt with at the start of the turn, chances are they will arrive in the final circle. We've been tracking them for a while, and it looks like they can get trapped in the storm and die in it if stuck long enough. Unlike henchmen and other NPCs, they don't die instantly and disappear when the storm hits them.
Marauders will be armed with a variety of weapons including rifles, pistols, and gas grenades which they will throw at you if you get too close. Armor and shield values seem the same as minions, so they don't take too long to kill.