Lion? If you’re a human in 40k you’re more likely to be a mangy street cat forced to work in a factory processing other cats into fancy feast. Fuck yeah I’ll be the Taus little pet over that, I can work in at a space turnip farm or something, maybe they’ll give me little human treats.
Really it was “If The Emperor Had a Text-to-Speech Device” blowing up on YouTube, imo, which spent alot of time shitting on the state of the Fandom and Games Workshop at the time (specifically voicing the absurdity of worshipping the Space Marines (fucking blueberries)). It got a lot of normal people I knew into the lore, which then cascaded into the wider public knowledge.
Unfortunately, because of Games Workshop vaguely gesturing at sueing all fan made content, they no longer do those videos. The good part is that instead they are doing parody/extremely intense drama around Hunter:The Gathering (which is Vampire: The Masquerade from the perspective of humans that know that there is more to the world), which is amazing and so fucking good.