In pretty much every software company, there is an existing codebase. And the daily job of the programmers in these companies is to build upon the existing codebase. And in pretty much all instances, the codebase is undocumented, tightly coupled together under narrow assumptions that no longer hold, brittle to the point that any small change will have an unforseen ripple effect in some dark corner of the code, and is generally a giant piece of garbage.
All day long, these programmers battle their way through the mountain of manure, simply trying to add some useless feature that some program manager thinks is important. All day long, they swear incessantly at the idiot who originally wrote the code. But they have no idea who this idiot is. Most probably, the idiot has long left the company, having moved on to build another codebase that will cause future programmers to think about jumping out the window. To most programmers, the author of the codebase is just some mythical figure that seems almost inhuman to them.
So who is this mysterious author of the world's legacy code? Who is this person that infects the codebase of every company across the globe? Nobody really knows. This person is known only as Coder Zero.