It’s a consistent recurring theme in their propaganda, from the grotesque racial caricatures in Nazi publications like Der Sturmer to the modern day, where they represent their enemies with hideous soyjaks and portray transwomen as not just men, but unwashed, hairy neanderthals.
I wonder if you could trace it back to criminal anthropology as outlined by Lombroso in his book Criminal Man which was basically a manual for using phrenology to do pre-crime (kinda an oversimplification but he’s completely wrong anyway so idgaf). Of course all the characteristics he described as “criminal indicators” were racial stereotypes, class markers, or so broad as to be applicable to anyone you wanted to shove in the mould.