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 a tarpaulin in front of Gordon, Percy and Emily. Molly ran away, embarrassed, until she learned that engines at the depot needed her empty 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.
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.
- 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.
- Molly is a mother figure to Thomas and a wife of Edward the Blue Engine.
- Home: Island of Sodor
- Train Built: Steamie
- Appearance: Yellow tender engine with 4 big drive wheels, black smokebox, silver buffers, red chassis, red lines around her sides, across her boiler, golden whistle,
- Personality: Shy, kind, nice.
- Gender: Female
- Alignment: Good.
- Allies: Thomas the Tank Engine (son), Edward the Blue Engine (boyfriend and husband) Henry the Green Engine (younger brother), Gordon the Big Engine (younger brother), [[James the Red Engine (nephew) Percy the Small Engine (nephew), Toby the Tram Engine, Duck the Great Western Engine, Donald and Douglas the Scottish Twin Engines, Oliver the Great Western Engine, Emily the Beautiful Engine (sister-in-law), Murdoch the Strong Engine (cousin), Arthur the LMS Tank Engine, Spencer the Silver Engine (sometimes), Mavis the Quarry Diesel, BoCo the Metropolitan Vickers Diesel, Bill and Ben the Saddle Tank Engine Twins (good friends and pals), Fergus the Railway Traction Engine, Annie and Clarabel, Old Slow Coach, Stanley, Stepney (grandson), Bertie, Terence, Butch, Trevor the Traction Engine, Caroline, Harold, Skarloey, Rheneas, Sir Handel, Peter Sam, Rusty, Duncan, Duke, Freddie, Mighty Mac, Luke, Bertram, Ivo Hugh, Rosie, Lady (beautiful magical friend), Belle (beautiful friend), Millie, Stephen, Bash, Dash, and Ferdinand the Logging Locos, Hiro (father), Flynn, Connor, Caitlin, Stafford, Winston the Red Car, Victor, Kevin the Crane, Dennis, Charlie the Purple Engine, Billy the Orange Engine, Salty the Dockyard Diesel, Porter the Dock Tank Engine, Harvey the Crane Engine, Elizabeth the Vintage Quarry Truck (sometimes), Cranky (sometimes), Jack, Alfie, Oliver the Excavator, Kelly, Ned, Buster the Steam Roller, Nelson, Paxton, Neville, Captain, Owen, Merrick, Hank, Flora, Pip and Emma, Jinty and Pug, Green Arrow, Iron Duke, Wilbert, City of Truro
- Likes: Working on the Fat Controller's Railway, engines who are friendly to her.
- Dislikes: Being laughed at, causing confusion and delay, icy tracks (in snowy weather)