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- “It's a shame you're not an elephant, Sidney."
"An elephant? Huh? Why's that, Whiff?"
"They say that elephants never forget!”
- ―Whiff and Sidney
Sidney is a forgetful blue diesel shunter.
In the seventeenth season, he was still on the hoist and was often referred to as a Christmas decoration by the other diesels, literally being used as one by Diesel 10 as well. Percy asked how long Sidney had been left up on the hoist and found out from Norman that it had been two years. Percy gave Sidney a new set of wheels as a Christmas present, and Sidney is now a really useful engine again.
In the eighteenth season, he, along with Diesel, Den, and Dart hid from Paxton, but after Paxton was unable to find them, Sidney, along with Den and Dart started to think that Diesel's joke went a little too far, but Paxton managed to find them again at the end of the day.
In the twentieth season, he was sent by the Fat Controller to collect new wheels for Percy. Sidney was worried he would forget his job and let Percy down, but Thomas, Annie and Clarabel suggested that he sing a song to remind himself what to do. Sidney thought this was a great idea, and started to sing his song, until he stopped at Wellsworth to talk with Gordon. After talking with him, Sidney completely forgot the words to his song, and, while trying to remember what he was supposed to do, ended up running all around Sodor, first to Whiff's Waste Dump, then to the Sodor Animal Park. Eventually, he decided that it would be best to go back to Knapford to confess to Sir Topham Hatt that he had failed to complete his special job, but upon arriving, he found a crowd of passengers waiting impatiently for their train to Brendam Docks. Thinking that taking the passengers was his special, Sidney found some coaches and took them to the Docks, where Sir Topham Hatt was waiting by Percy's new wheels, grumbling about the forgetful diesel's lateness. When Sidney arrived, the passengers praised him, and Sir Topham Hatt reminded him that he still had to take Percy's wheels to the Steamworks. Sidney, who thought he had already completed his special, gladly accepted the supposed second special, and took the wheels to the Steamworks, where Percy was waiting.
Sidney is a very helpful diesel engine, but he's also very forgetful. He starts his day at one location and ends up at another, not remembering how he got there. When it was his turn for repairs at the Dieselworks, he was hoisted up and had his undercarriage removed. Being patient, Sidney was happy to wait, and wait, and wait. He sat there happy to pass the time with any engine that happened to be visiting. Two years later, he still had no wheels, so Percy helped him at Christmas to get a new set of wheels and now he is back on track.
Sidney is based on a BR Class 08 diesel-electric shunter. Over seventy members of this class survive today in preservation, while around 100 remain in service on the national rail network. They were in fact the most successful shunting engines in the world, with 996 of them built. Diesel , the Diesel Shunter, Paxton , Splatter, Dodge, 'Arry, Bert, Ulli and The Mainland Diesels are also members of this class.
Sidney is painted navy blue with yellow lining and hazard stripes under his face. His coupling rods and front bufferbeam are painted a rusty orange colour. His paint is chipped in places, and shows signs of weathering.
- Kerry Shale (UK/US; Day of the Diesels only)
- Bob Golding (UK/US; seventeenth season onwards)
- Nicolás Frías (Latin America; seventeenth season onwards)
- Shōto Kashii (Japan; seventeenth season and The Great Race only)
- Ken Sanders (Japan; eighteenth season only)
- Tomohiro Tsuboi (Japan; twentieth season onwards, excluding The Great Race)
- Grzegorz Kwiecień (Poland; seventeenth season onwards)
- Helge Winther Larsen (Norway; seventeenth season only)
- Bruno Marçal (Brazil; seventeenth season onwards)
- Mariano García (Spain)
- Denis Bespalyy (Russia; seventeenth season onwards)
- Jukka Voutilaninen (Finland; Day of the Diesels only)
- Zvika Fohrman (Israel)
- Oliver Warsitz (Germany; seventeenth season onwards)
- In some merchandising and books, Sidney's name is misspelled as "Sydney."
- Despite Sidney's nickname being "Sid," he has been consistently referred to by his full name rather than his nickname. He shares this dilemma with Norman and Paxton.
- For an unknown reason, Sidney travels at a slower pace than the other Class 08's on Sodor.
- In Big World! Big Adventures!, Sidney gains a headlamp.
- “Sidney, how long have you been up there?"
"Erm, not very long Percy. I mean.. er.. I forget."
It's been about two years!"
"Two years?! That's a very long time."
"Yeah, I'm waiting for my wheels. I think the order's been misplaced.”
- ―Percy, Sidney, and Norman discussing how long Sidney has been on the hoist waiting for new wheels, The Missing Christmas Decorations, seventeenth season
- “Ha ha ha, he he he, a very special job for me.
All the way to Brendam Docks, to fetch a very special box!”
- ―Sidney singing his song, twentieth season
- Take-n-Play (“discontinued”)
- Wooden Railway (normal version. Holiday and Seaside versions discontinued;)
- Classic Minis
- Chillin' Minis
- DC Super Friends Minis (as Mister Miracle and The Penguin)
- Sweets Minis