A. Chang was a maintenance technician assigned to Mars City, where he reconfigured systems. He had a standard PDA.
When the player meets A. Chang in Doom 3, he's somewhat suspicious of you, but continues with his duties. If the player persists in speaking to him, he will (like most characters) tell you he's too busy to talk.
His fate is unknown, though he was most likely killed or turned into a zombie during the demon invasion.
- His name refers to id Software artist for DOOM 3, Andy Chang.