A model of Texas Instruments calculator initially designed to DEVOUR PUNY HUMANS.
It had the uncanny capability of determining human caloric value. This was originally for risk evaluation--the greater the caloric value, the more worthwhile the target was.T-rex could level buildings without effort, and was guaranteed to destroy a conspicuously Japan-like nation in 10 minutes in simulations. It was also to be 100 feet tall, and capable of grappling any nubmer of oversized, nuclear radation-induced mutated monsters.
However, funding was cut before any of the structual components could be designed. Unfortunately, the megalomaniac (Specifically, the male 45-60) demographic demanded large swarms of smaller, more efficient robots, due to the rising prices of oil, thus leaving TI with the problem of what to do with their reseearch.
In order to cut its losses, TI instead made a smaller, less effective model, with absolutely no firepower and marketed it to archvillain children. It was small and poorly made, and only contained the aforementioned calorie-calculator.
Also, when dehydrated to its more formal "Trex", a brand name of "cooking fat" much loved in the late 70's (Viciously anihalated by protesters later on.) Please do not be confused with the legendary "Carry On (tm)" joke as to the name of one's feline.