Who or what is BigRat?

^This Chonky Boi (he's also the background, if you haven't noticed).

What is this site?

The site bigrat.monster expires soon and won't be reachable anymore sometime in 2025, see this for context.
This site will act as a hub for everything bigrat-related and shall preserve it for generations to come.

While there already are differant sites imitating bigrat.monster, there is no fanclub (or one that has a web presence).