Could be misremembering, but IIRC it was called Compiler Explorer and used to live only on a subdomain of godbolt.org. But, it was so useful that it became presumably vastly higher traffic than the personal homepage part and people often referred to it as just "Godbolt" probably because it sounds cooler and is shorter than saying "Compiler Explorer" (and it may not be obvious the domain name is a last name rather than just a cool name for something.)