I read your username as your comment at first, so now you’re Kevin as far as I’m concerned.
(TOS spoiler for one episode)
Just in case any lurkers are still wondering: I think - but don't remember 100% - the guy everyone's calling Kevin was some random crew member in TOS who took over the ship's control room and started trolling the ship's PA system, until the main characters managed to break into the room and subdue him.
The episode gave him an unreasonably long monologue with the PA system, during which he sang an entire song ("I'll Take You Home Again, Kathleen"). It's also a little weird that this one crew member can take over the entire ship even though he's some average joe who we don't really see again.
No idea where the memes about him started though.
I didn't know I knew about risa but only when i went to the original site (instead of kbin). as a tng fan this instance heals my broken body