What’s up with the titles

Okay so I’ve been seeing the titles everywhere and I’m just wondering how they work I know a couple people have their mains as their titles like “killers name” main or P100 “killers name” and I’m just woundering how you get the titles like the first one as the current one I’ve got is for wesker or at least something relating to him, and I quite literally had my last game of killer as him and found it holy shit how in the so I’m just wondering what deal with them is weather their mod givin like the p100 or use reddit to read what killer you just played as and have the title as that. Again I’m not sure and would love some clarification from someone on it