The Gate Guardian is a Euclid/Keter class humanoid entity that is one of many potential entities that share the SCP-001 title. It can be viewed as one of an overarching protagonists of the entire mythos. SCP-001 is the being that prompted the SCP Foundation to exist. He said one word that echoed through the administrator's head, "prepare". It was that one word that made the administrator create the Foundation for an unknown future event and to contain many other dangerous or helpful entities