The Aperture Science Handheld Portal Device, often simply referred to as the Portal Gun, or its acronym, "ASHPD", is an experimental tool used to create two portals through which objects can pass. The central piece of the "Portal project", Tier 3 of the three-tier program created by Aperture Science's CEO Cave Johnson on his deathbed in 1976, it is used within the Enrichment Center's Test Chambers, as the Test Subjects' primary tool to complete each chamber.