I always wondered this, but never got a straight answer. Some people would say that he was extremely racist, and some people say that he believed in racial equality. Some people were in-between and said that he believed in racial equality, but held prejudice towards certain ethnic groups (Jews are the ones I’d see mentioned the most). I’ve heard mostly positive things when it comes to Joseph Stalin and his views on race, but I never went too in depth.
Was Josef Stalin personally a racist? written by u/rusoved talks briefly about this, namely anti-Semitism
The other answer is a good general overview of Stalin's prejudices as a person, but I find it a little light on examples of policy before WW2. Though I don't talk about Stalin directly, I go into some more depth on his pre-war policies and how they affected ethnic others in the USSR in this answer here. I don't feel very comfortable making statements about Stalin as a personality, but I am willing to say: I think it's clear that he both believed he was committed to racial equality, while operating under a rather narrow and Eurocentric understanding of "advancement," and that his fear of foreign meddling could easily lead him to authorize and promote xenophobic and deadly policies.