Derek is a jolly, enthusiastic Diesel engine, who was brought in to assist Bill, Ben, and BoCo at the China Clay quarry. Unfortunately, due to his engine, he is highly prone to teething troubles, namely overheating and suffering frequent breakdowns, for which he is apologetic for the inconvenience. As a result, he spends many a day having his engine tended to. But Derek is a likable chap and even Bill and Ben decided that they liked him due to his friendly nature. Derek has an infectious charisma, is keen to help anyone around him, and has a passion for sorting things out in a jiffy - if his cooling system lets him.