Emily is a large Stirling Single tender engine.
When Emily was new to Sodor, she was ignored by the other engines for Annie and Clarabel without Thomas' permission or knowledge. The matter was resolved after she saved both Thomas and Oliver from a nasty accident on the cross-points, and she was rewarded with two new coaches. Emily proved to be kind-hearted, as she was the only engine concerned about Henry when he was ill due to leaky tubes.
However, Emily has proven to be a nuisance as she bossed everyone about when they were clearing up after a storm, Thomas when taking passengers, and Percy when shunting trucks. When pulling the express for the first time, she was determined to keep to Gordon's timing, only to run out of water.
When Thomas had to stay at Knapford Sheds, Emily did not like his company at first as she just wanted some sleep. However, she learned how comfortable it is to have the company of friends and once Tidmouth Sheds was rebuilt, she was transferred there to be with her new shedmates.
Like most engines, Emily can get quite puffed up in the smokebox. When she was called "Excellent Emily", she ignored the advice of Murdoch, Thomas, and Duck only to get herself into trouble. Afterwards, she took their advice to get her job done.
Emily tries her best to make her friends happy. When she assumed that Mavis was sad, she took flowers to the quarry, but only created a mess. When she tried to help her friends with the football match, she neglected to fetch the dirty washing, which turned out to be the football team's uniforms. Also, when the Fat Controller lost his top hat, Emily went to find it without success and then took the special Christmas train without permission. However, she always makes amends for her friends' sake.
In the seventh season, Emily acts as a sisterly figure to the others. Emily is kind and friendly and always sensitive to the other engines' feelings. If she wrongs someone, knowingly or not, she is quick to apologize. From the eighth season onwards, however, Emily can tend to get into trouble because of her fussy and bossy attitude, but she is nicer than she lets on.
Emily is based on a GNR G Stirling Single, of which there is only one left in the world, located at the National Railway Museum in York.
Emily is painted in the emerald livery of the Great Northern Railway with gold lining and chocolate running-boards.