In the first century CE, there were two social classes in which a gladiator might fall; the auctorati were free people who voluntarily became gladiators and the damnati were slaves forced to train at a ludus (gladiator school) and fight in the arenas. Either way, being a gladiator meant that you were a part of the lowest rung of Rome’s social order. Neither class could vote, leave a will, or testify in court.
Gladiators were bound by oath “to endure to be burned, to be bound, to be beaten, and to be killed by the sword” according to Petronius, which essentially meant they were property for their masters to do with as they pleased. Disobedience and belligerence carried a variety of punishments, like lashing or branding. Particularly rebellious slaves who were granted their freedom were marked as dediticii and forbidden to come within 100 miles of Rome upon penalty of reenslavement. If a slave was condemned to be executed, crucifixion was often employed.
Pollice Verso by Jean-Leon Gerome, a famous gladiator painting wherein the winner is looking to the games’ patron to tell him whether or not to kill the poor soul he’s vanquished. Source
Being slaves, they had no choice of diet. While you might think that owners would feed them hearty protein to build muscle, they were actually involuntary vegetarians who ate mostly barley, oatmeal, ash, boiled beans, and dried fruit. This fare was basically the same ingredients you would find in pig troughs and it’s clear that the owners of the gladiators fed them thus because it was cheap and filling.
In this mosaic, a Secutor named Astyanax fights with a Retiarius named Kalendio. The null sign above Kalendio’s image means that he lost the match and was killed. Source
In addition to fighting, gladiators could be rented out by their masters (who had the same social status as a pimp) to serve as bodyguards or as sex workers for high paying noble johns and janes. Only in the fevered, bloody spectacle of the arena, it seems, were gladiators cheered.