He was at the main gate when the Third Doctor, disguised as a milkman, attempted to enter the facility. When the guard asked him where "the other bloke" was, the Doctor told him that he was sick. The guard then allowed him to enter the facility.
Like most Global Chemicals employees, he had been brainwashed by BOSS. During the final phase of BOSS' plan to link human minds into itself, the guard was told by Stevens to stay at the front gate and prevent anyone from entering. The Doctor managed to get past him when he "shut down" and stood still during a lull in the linkup process. He was still standing there when the Doctor came rushing outside later, and the Doctor tackled him to the ground to save him from the exploding building. (TV: The Green Death)