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Eiri Masami was a programer at Tachibana Labs, and one of the workers on the development of Protocol 7. While coding the new protocol, he added code that would allow humans to connect directly, without devices, via Earth's natural "brain waves" (The Schumann Resonance). When Tachibana got wind of this, they threw Eiri out of his job and he shortly after killed himself in a train yard.
However, this is not his end. He uploaded his personality into the Wired and lives there as it's god. He is behind the actions of the Knights of Eastern Calculus, who he considers his believers. He attempts to convince Lain that HE is her creator and that she too is his follower. However, Eiri is not the Wired God (Lain is) and he eventually loses everything when Lain refuses to believe in his godhood.