(I don’t know if Aristotle owned slaves. I’m just saying that chances are, amongst the ancient Greek philosophers, there were quite a few slave owners, and nobody makes a big deal of that)

You’re in luck, Aristotle was indeed a slavery apologist, if not a slaver himself:

https://en.wikipedia.org/wiki/Natural_slavery

He who thus considers things in their first growth and origin, whether a state or anything else, will obtain the clearest view of them. In the first place there must be a union of those who cannot exist without each other; namely, of male and female, that the race may continue (and this is a union which is formed, not of deliberate purpose, but because, in common with other animals and with plants, mankind have a natural desire to leave behind them an image of themselves), and of natural ruler and subject, that both may be preserved. For that which can foresee by the exercise of mind is by nature intended to be lord and master, and that which can with its body give effect to such foresight is a subject, and by nature a slave; hence master and slave have the same interest.

Seeing then that the state is made up of households, before speaking of the state we must speak of the management of the household. The parts of household management correspond to the persons who compose the household, and a complete household consists of slaves and freemen.

Where then there is such a difference as that between soul and body, or between men and animals (as in the case of those whose business is to use their body, and who can do nothing better), the lower sort are by nature slaves, and it is better for them as for all inferiors that they should be under the rule of a master.

Aristotle sought to reinforce the idea of slavery as inherent to the natural order of the world; that some people were pre-defined to be slaves by innate characteristics that separated them from a “master”-class (of which he was a member).

(Source for quotes: https://historyofeconomicthought.mcmaster.ca/aristotle/Politics.pdf)