The OG leaker afaik, Spanish dude, probably works for Shueisha in some capacity (might be on the Spanish translation team but this is me speculating)
Basically, he has access to very early leaks due to his longevity in the fandom. He's been reliable over the years and, afaik, doesn't troll or give out fake leaks ever. If he confirms something than that's happening 100%.
Why he's sensitive?
Some chads leaked the last chapter earlier than he did. He got pissed they stole his spotlight and started pouting. This happened once or twice before, too. His excuse is that it's too early to leak a chapter before he does it because Shueisha will get mad or smt. Ironically his plan was to post the full summary of 1054 just a day after it was leaked, to his chagrin.
Nobody really fears him lmao and there's no reason to. He's just the leading weeb in our community of weebs. Not a sought after title imo