Elevator Security Guard

The Security Guard sits in the lobby of the Empire State Building. It's unknown if he is a mortal or not.

The Lightning Theif
He first appears when Percy returns the Master Bolt to Zeus. When Percy shows him the Master Bolt he fumbles for his key card and tells him to insert it in the security slot.

The Last Olympian
He (persumably) appears again when the Demigod Army tries to go up to Olympus. Again he says there's no 600th floor, but when Percy says that "Forty demigods attract an awful lot of monsters. You really want us hanging out in your lobby?" He then hits a buzzer and the security gates swing open. Later when Kronos enters the lobby the guard is gone.

Appearance
He has pale blue eyes and a bald head.