In the days of ancient Rome, there were battles that were not for the recreational use of the fighters but for the viewers and these were battles to the death. These battles were fought by the gladiators, they were the bloodiest battles that were every held. Two or more people would fight to the death; the ones that won still weren't winners, as they would normally unleash lions on them to finish them off.
They normally were given a choice of what they wanted to fight with, a lot of them took swords and shields but you could have seen some people fight with different kinds of weapons like flails, spears, maces, etc. So being a gladiator was something that most people did not want to be. Most often you did not choose to be gladiator, but you were told to become one. They were mainly war criminals, slaves, and prisoners and were taken by what they call a lanista. This lanista was a person who would buy these people and turn them into gladiators.
Then the lanista would rent them out or sell them to rich people so they could watch them fight in the arenas. One thing that a lot of people wonder today is whether or not a woman could become a gladiator. You may find this odd, but women were often chosen to be gladiators as well. They could become gladiators if they wanted to; which would have been rare. It was far more likely that they would have been chosen just like most male gladiators. This ended during the reign Emperor Septimus when he banned them from being gladiators because he didn't feel right putting woman in harm's way and watching them die.
To become a gladiator you had to go to a school this school was known as the gladiator school where they taught you how to defend, attack, and fight with many different weapons. Even though most gladiators were killed at the end because they were mainly criminals it was important that they knew how to fight so that they didn't die immediately when entering the arena. There were also people who volunteered to become gladiators to gain prizes for winning and to increase their fame by winning battles. When you became a gladiator there was no turning back, you fought until you died or the audience would vote for you to be set free to live your life or die. There were times that prisoners could get this but for the most part they were killed by lions or locked back up to fight again.