1 Dustin: Okay, so none of us are thieves. What classes are we? Eleven is clearly a magic-user.
2 Mike: I think we’re all level-zero nobodies.
3 Dustin: You know what happens to zero-level characters? Retainers and hirelings? They all die in droves!
4 Lucas: Can I be a fighter and hit him?
4 Mike: Be my guest.

In many roleplaying games, particularly those based on ideas originated by Dungeons & Dragons, player characters begin the game as "1st level" characters. This indicates that they have entered their profession as a fighter, thief, magic-user, whatever, and had some initial training, but they are essentially raw and unexperienced. As they take part in adventures, slaying monsters and gathering treasure, they become more experienced and after a while rise to the rank of "2nd level". At this point the character gains some new abilities and/or improves some existing ones. They may be able to soak up more damage in combat, or have a better chance to hit foes when attacking, or gain additional spells that can be cast, and so on.

As the game progresses, characters continue to "level up". If a game lasts long enough, characters may reach the lofty heights around 10th or 20th level, which, depending on the exact game and rules set being used, means the characters now possess abilities that mark them as amongst the most powerful and heroic people in the land. In some cases this may involve powers close to demigod level and the characters may challenge actual gods or other ultra-powerful entities.

But there is also room at the bottom end of the scale. If "1st level" refers to a fighter who has had some training and is ready to swing a sword at goblins, or a wizard's apprentice who has learnt to cast their first magic spell, then what about the vast majority of people who don't know how to do any of those things? Whose only potential fighting experience might be that they got into a bar room brawl once?

These people are often referred to as "0 level" characters. They have some skills and abilities, but less than those special "1st level" characters. Zero-level characters are not worthless though. They represent farmers and craftsmen and traders and other things. In a pinch, they could pick up a weapon and swing it, but not with as much success as a trained first level character.

In some games—particularly early editions of Dungeons & Dragons—some of these zero-level characters were available for hire. The player characters could hire retainers and men-at-arms with rudimentary training to accompany them on their adventures, for various jobs such as looking after the horses, or holding torches inside a dungeon while the PCs battled it out with goblins, or hauling back sacks of treasure. These zero-level hirelings would earn a small retainer fee, plus often a half share of any treasure recovered. But they also faced risks. Retainers could be used to scout ahead... Now here think about that guy at the start of Raiders of the Lost Ark who tried to go ahead of Indy, or the one the Nazis used to explore the Path of God in The Last Crusade. Yeah, the ones who got killed by the traps.

In some early D&D games, zero-level hirelings were used essentially as cannon fodder, taking risks that the player characters didn't feel like facing. And yes, they tended to die in droves.