Hugo is unique for being fitted with a propeller. He is a very fast engine, whose spinning propeller makes him very popular with passengers.
Upon arriving on Sodor, he surprised many engines and Sir Topham Hatt with his fast speed. Stephen, however, told Thomas that he may replace them. This made all the engines unfriendly with him and it wasn't until Hugo explained to Thomas and Percy that Stephen was wrong. He wasn't replacing the engines; he doesn't even have a coupling hook to pull coaches or trucks. This helped the engines learn that Hugo is actually very nice and later they gave him a proper welcome.
He would later see a real zeppelin in the sky and felt upset that he couldn't fly like it. He followed it all over the island and was so keen on flying that he forgot to turn off his propeller upon entering Knapford's platform. Sir Topham Hatt explained that he's a rail zeppelin meant to travel on the rails and not in the sky.