A security guard was an individual employed by an organisation to provide security.
Security guards were commanded by the Security Chief. (TV: The War Games)
Sean Flannigan was a security guard aboard the Wheel. (PROSE: The Wheel in Space)
The Pharm had security guards. Jack Harkness remarked that grey was not "their colour". (TV: Reset)
There was a security guard in a school in Philadelphia by 2008. (PROSE: Silver-Tongued Liars)