So do neither "slave" nor "slaver" exist as possible character background options in your game?
I suppose it's possible in a setting that doesn't have anything remotely resembling a faux-Roman or faux-ancient-Greek or faux-ancient-Egyptian culture, or faux-several-other-cultures where, historically, slaves and slavery were a culturally accepted thing.
There have been a lot of times and regions in history where "hard" slavery wasn't a culturally accepted thing.
"Soft" slavery - i.e. indentured servitude, debt slavery/servitude, prisoners being made to work (which is, frankly, an undeniable form of slavery), serfdom (which can sometimes be harsher than stuff actually called slavery - though it is rare), and so on is almost ever-present in human history, up to and including the present day (though it has been reduced significantly compared to say, 50 years ago).
Re: Egypt there's increasing evidence that a lot of people we assumed were slaves because of historians operating under an assumption that ancient Greece and Rome were the "model" for all ancient societies, were not, in fact, actually slaves. They might have been fairly low-paid, but it seems like an awful lot, maybe the majority of "slaves" in ancient Egypt were in fact just workers.
As most D&D-style fantasy settings focus largely on quasi-Medieval settings where "hard" slavery was not a cultural norm, it's not surprising that it's pretty easy to cut it out of most. You can have absolutely ghastly settings without it.
Largely because of situations and places where the slaves (sometimes vastly) outnumbered the free.
Worth noting that these situations/places were very rare historically until the 1700s.
In ancient societies most situations with "hard" slavery featured 5-20% of the society actually being slaves (including the softer forms of slavery, like temporary debt slavery). Even in classical Rome, which insane influxes of slaves at times, across the empire I believe it was below 20% at all times, with only certain regions within the empire going higher, and then to like, 40%. That's not to say it wasn't truly horrific - Roman mass-enslavement was completely beyond words in its horror. But you didn't get the like 8:1 slave-free ratios you got in places like Haiti until much, much later.