Jaspers

The Unnamed Security Guard is a minor character in Grand Theft Auto V, who appears only in the Prologue mission.

Before The Prologue
Prior to the events of the Prologue, he will have worked for the Bobcat Security bank in Ludendorff, North Yankton for an unknown period of time.

Events Of The Prologue
During a heist of the Bobcat Security bank he works at performed by Trevor Philips, the then-Michael Townley and Brad Snider, he sneaks up on Michael, holding him at gunpoint, threatening to shoot him in the head if they don't give up the heist, removing Michael's mask. After being advised by Michael to forget what he saw and leave, Trevor shoots him in the head, killing him instantly.

Trivia

 * Chronologically, the Unnamed Security Guard's death is the first on-screen death of the HD Universe.