Whiff is a grubby green tank engine who collects rubbish. His main task is collecting rubbish and scrap, which explains his dirty appearance and smell.
When Whiff first came to the railway, Emily was asked to help him out. Emily was under the impression that he would be more intriguing and that the task would be more exciting; Emily was eager at first, but disappointed when she learned that Whiff worked with rubbish. Emily tried to avoid being seen with him, but Whiff found her almost everywhere she went. Although the two were mocked by other engines wherever they went, Whiff maintained a cheery expression and seemed either not to notice or care. When Emily finally escaped from Whiff, she found Spencer blocked by a long line of trucks full of rubbish. When none of the other engines helped, she found Whiff. Emily apologised to Whiff, and together they cleared Spencer's line.
One day, Whiff was meant to take away a truck of old cans from a siding. Toby, who was looking for something special to present to the Fat Controller, mistook the distant truck at first for something valuable. Later, Whiff brought the Fat Controller to a broken-down Toby, who had discovered a sign belonging to the old Sodor Tramways.
Whiff now runs his dump with help from Scruff. One day, when Scruff's "scruncher" was broken, Whiff stayed with him at the Sodor Steamworks until he was mended. This left the rubbish dump without anyone to run it, so Gordon was put in charge for the day.
Whiff requires help from time to time with his rubbish trains. Once, Thomas was supposed to help Whiff with his train, but only succeeded in crashing into the trucks at Wellsworth as Thomas was trying to stay clean for the Duchess of Boxford. In the end, Whiff took the Duchess whilst Thomas cleared up the mess and took the rubbish train. Later on, Whiff tried to be as grand as Spencer by hauling heavy loads. He helped Emily and Edward by taking some of their loads, but only neglected his own job of clearing the railway of the rubbish trucks. After delivering the respective loads, Whiff carried out his work and proved once again to be really useful.
When Bradford arrived on Sodor, Whiff used him as his brake van to take dirty trucks filled with waste. However, Bradford refused to move as the trucks needed to be cleaned, causing Whiff to be late.
Whiff is cheerful and optimistic. He enjoys his job of collecting rubbish. He either does not seem to care what the other engines think about him or is oblivious to their opinions. Despite that, he is friendly and always does his job well at the Waste Dump. He is somewhat naive, as he did not realise why the other engines tried to avoid him so much. However, in Misty Island Rescue, he is shown to know a bit about Sudrian history, since he knew about the tunnel connecting Misty Island to Sodor.
According to Whiff's TV series designer, Whiff can also be described as "nerdy".
Whiff is based on the North Eastern Railway's 2-2-4T No. 66, named "Aerolite". Aerolite was built in 1869 to replace a destroyed Kitston locomotive of the same name, and to haul the Mechanical Engineer's saloon coach. It was rebuilt exstensively several times during its career. It was classified X1 by the LNER in 1923 and was retired in 1933, being preserved at York the following year. It can be found today at the National Railway Museum in York.
Whiff is painted in a dark green livery with black and yellow lining and green wheels. He has red numberplates on his bunker. He wears large spectacles on his smokebox.