Harrison is a facsimile construct copy of a human working in the clerical staff at the Pentagon in the United States of America, as part of Ramjet's long term infiltration plans. Made from inferior equipment compared to other Decepticon facsimiles, Harrison has an extremely limited ability to communicate via speech, and has a short life span. Still, his co-workers don't seem to mind, putting down his limitations to the real Harrison having graduated from an undistinguished educational institution in California.
IDW comics continuity
After discussing the relative failures of both Megatron and Starscream with Skywarp, Ramjet boasted he was more capable than either of leading the Decepticons. Skywarp gave him 24 Earth hours to come up with a good plan before he would follow him. Ramjet contacted Harrison at the Pentagon, instructing his dim-witted artificial minion to meet him at their prearranged location with the codes to the United States nuclear missile arsenal that Harrison acquired the previous week.
The next morning, a severely malfunctioning Harrison crashed his car through the forest to the meeting point with his master and handed over the missile codes. Ramjet realized Harrison's life was soon at an end, but instructed the construct to return to work, for he may have need of him later. As Harrison stumbled off, Ramjet boasted on his grand scheme to control the Decepticons, the humans and strip the Earth bare of its resources. Unfortunately, Harrison's life span wore out and he collapsed into a smoking wreck. Ramjet didn't care.
After Megatron destroyed Ramjet, he dropped the traitor's right arm on Harrison's office at the Pentagon.