Molly is a powerful, bright yellow tender engine.
When Molly first came to the railway, Emily laughed at her for hauling "empties", empty trucks she (Molly) was pulling due to not having deliveries to make. Molly's feelings were hurt, so Thomas came up with an idea. He had workmen decorate Molly's trucks with lanterns and cover them with tarpaulins, to make them look special to the other engines. The wind, however, blew off the covers in front of Gordon, Percy and Emily. Molly ran away, embarrassed, until she learned that engines at the depot needed her trucks to carry coal. When Molly arrived at the depot, Edward, Henry and James were grateful to see her; but Gordon was annoyed when he had to wait at a signal for Molly's and Thomas' trains to pass.
When Emily had to work with Whiff, Molly was one of a number of engines who laughed at her. Later, Molly helped James with the removal of pipes on the line during a busy winter and then, she advised Thomas to slow down when he was taking a sailing boat for the Mayor of Sodor.
In The Great Discovery, Molly received news from Bill and Ben that Stanley had found Thomas.
Molly is a powerful, bright yellow steam engine. She is proud of her strength and is happy to put it to use as one of Sodor's bigger engines. She often works pulling empty trucks to the coaling plant. Because she is a sensitive engine, she often worries about fading into the background. Sometimes taking "empties" makes her feel less important and sad, but in the end, she will usually see that taking "empties" is a vital part of operations and an important task after all. Molly has a peacekeeper attitude, tends to be rather sensible, and is looked upon as a "big sister" by some of the other engines. However, she is a sensitive soul, who can be easily embarrassed and can get upset by conflict, and will steam away to avoid it, but will usually have the courage to do what she thinks is right. Molly likes to be as good as everyone else and wants the other engines to think the best of her.
Molly is a Great Eastern Railway D56 Claud Hamilton. Claud Hamiltons were built at Stratford Works from 1904 to 1911.
Although Molly keeps the GER standard sized 7-foot driving wheels, she has a large 4' 9" boiler, Schmidt superheaters and a Belpaire firebox. Her cab is fitted with two side windows. She has a Great Northern-style chimney, a flat firegrate and a variable blastpipe.
Molly is painted yellow with grey and red stripes and brass boiler bands.
- Season 9 - Molly's Special Special, Thomas' Milkshake Muddle (cameo), and Thomas and the Golden Eagle (cameo)
- Season 10 - Big Strong Henry (cameo), Sticky Toffee Thomas (cameo), Emily and the Special Coaches (cameo), and Thomas and the Birthday Mail (cameo)
- Season 11 - Emily's Rubbish (cameo), Henry's Lucky Day, and Thomas Sets Sail
- The Great Discovery (does not speak)
- Keiko Nemoto (Japan)
- Blanche Ravalec (France and French-speaking Canada)
- Molly appeared with a larger face in promotional shots and in certain Thomas and Friends magazine stories. This is assumed to be a prototype face, as it was never used in the television series. The face was also used on her Take-Along card, and all merchandise lines except for the Wind-up line.
- On the newly designed Official Website, Molly's promo has her large face.
- One of Molly's models is currently on display at Nitrogen Studios.
- Molly's whistle is a higher pitched version of Gordon's.
- According to The Big Book of Engines, Molly's nickname is 'Molly the Mighty!'
- Even though Molly's tender wheels are black, most merchandise ranges have them yellow, except for TOMY and TrackMaster.
- Wooden Railway (normal and talking)
- Take Along (normal and metallic; discontinued)
- Motor Road and Rail (discontinued)
- TrackMaster (normal and R/C; R/C discontinued)
- My First Thomas
- My Thomas Story Library (discontinued)
- Wind-up (Japan only)
- Switch-On Keychains
- Bath Toys