Nelson's job is to carry construction workers and the Pack vehicles to and from work sites. As the bearer of such weighty loads, he often feels overworked, but never complains.
In his first appearance, Jack asked Nelson if he was the most important, as Patrick boasted that he was the most important earlier. Nelson told Jack that he is the most important, as he is the main source of transportation. Later, when a fierce storm raged across Sodor, Nelson and Oliver were sent to clear Henry's Tunnel.
However, Nelson soon got tired of always having to carry the other machines to and from work. He began dreaming about being carried himself. The next day, Thomas came off the rails and broke a wheel. So Nelson was sent to take Thomas to the repair yard. When this was done, to his surprise, Percy carried Nelson back to the yards on a flatbed. Nelson had a splendid ride, and it was as magical as he had dreamed.
Nelson is a clever, intelligent, and wise ballast tractor who often feels overworked but never complains. He is proud of his paint and is happiest when he looks his best. Although he will never offer up a complaint, he is the first machine to comment on what is going wrong on the construction site.
Nelson's front strongly resembles a Scammell 15LA ballast tractor. His rear resembles a 1927 Scammell Pioneer tractor unit.