Diesel 10, or simply Diesel, is an evil diesel engine with a semi-sentient roof-top, hydraulic claw, which he has named "Pinchy".
Thomas & the Magic Railroad
Diesel 10 once visited the Island of Sodor a long time ago, and caused trouble for the steam engines while he was there. During his visit, he found Lady, the engine responsible for keeping Sodor alive, and chased her, making her crash. Following the accident, Lady's caretaker, Burnett Stone, hid Lady in his workshop and tried to restore her, but failed to bring her back up to steam.
Several years later, Diesel 10 came back to Sodor when the Fat Controller was on holiday, intending to destroy Lady forever. He was first seen by Thomas and Gordon when he raced past them at Killaban Station, and brought his two lapdogs, Splatter and Dodge, to the railway, who were present when he was scheming. He caused several problems for the steam engines, such as dumping sneezing powder around Tidmouth Sheds and later destroying the scaffolding that had been placed beside the shed.
When Mr. Conductor travelled across Sodor to find the windmill, Diesel 10 found him and held him over the Big Dipper, intending to drop him. However, Mr. Conductor managed to escape by cutting one of the hydraulics hoses to his claw with a pair of wire cutters, causing him to fling Mr. Conductor across the island and to the windmill. Diesel 10 was later present at the Coaling Plant, where he was covered in coal when he was teaching Splatter and Dodge “how to stop being stupid”. After Junior flew in the air after riding the windmill's sails, he landed on Diesel 10's cab, who raced across the island and to the smelter's yard, where he tried to push James and Junior into the melting pit. Fortunately, Junior and James managed to escape by using the last of the former's gold dust.
After Lady was brought back up into steam and returned to Sodor, Diesel 10 found her and began to chase her, Thomas, and Burnett across the island, until they reached the viaduct, but not before Splatter and Dodge betrayed him. Lady, Burnett, and Thomas managed to cross the viaduct safely, but Diesel 10 was too heavy for the rails and plunged into a barge of sludge below the bridge, and was sent away in disgrace.
Thomas & Friends
Diesel 10 later returned to Sodor years later under unknown circumstances. It can be assumed, however, that Sir Topham Hatt decided to give him a second chance. He was seen working at the scrapyard, loading piles of scrap into trucks. The very sight of his return caused Thomas and Percy to shudder in fright.
When the steam and diesel engines were holding a meeting at the coaling plant so that they could work on the Sodor Airport, Thomas was sent to the scrapyards to inform Diesel 10 of the meeting. However, Thomas was too frightened to meet Diesel 10 again, and sped away as fast as he could, not believing that Diesel 10 would want to help the steam engines due to their difficulties in the past.
Soon, the airport was nearly complete with its construction, until a water tower collapsed, cracking the runway and blocking the line. With Harvey all the way on the other side of the island, Thomas went to ask Diesel 10 for assistance. After some slight hesitation, Diesel 10 agreed to help clear the wreckage.
After Thomas was found prior to the reopening of Great Waterton, Diesel 10 was among the diesels present at the quarry when they heard the news. Later, when the Sodor Search and Rescue Centre was opened, Diesel 10 was present at the rescue centre's grand opening, standing on a cliffside overlooking the rescue centre and the steam engines below, threatening to return.
When Percy was experiencing a falling-out with Thomas, Diesel 10 decided to manipulate him into helping him restore the Vicarstown Dieselworks, by having him visit the Dieselworks and befriend him. Diesel 10 managed to convince Thomas to arrive at the Dieselworks, where he was held hostage while he, Percy and the other diesels went to the Sodor Steamworks. Once there, Diesel 10 betrayed Percy and took over the Steamworks. Percy returned to the Dieselworks to rescue Thomas, when he noticed that sparks from Pinchy had set the main building ablaze. Percy brought Belle and Flynn to put out the fire. After Thomas was saved and the fire was put out, Percy, Kevin and the rest of the Steam Team went to the Steamworks. After a brief argument with the diesels, Sir Topham Hatt arrived and, after being told about the state of the Dieselworks, agreed to have the place restored. Diesel 10 and the other diesels worked alongside the steam engines to restore the Dieselworks, and he became the new head of the Dieselworks, with Den and Dart taking over in his absence.
When it was Christmas time, Diesel 10 became jealous of the steam engines for having more decorations at Tidmouth Sheds than he and the diesels had at the Dieselworks. He began stealing decorations from the sheds to bring to the Dieselworks, enlisting a reluctant Paxton to help him. Diesel 10 was caught by Percy, who chased him back to the Dieselworks with the rest of the Steam Team, where Diesel 10 found out that Sir Topham Hatt had, in fact, had Paxton deliver some decorations to the Dieselworks, so he gave the decorations back to the Steam Team. But as most of them had been damaged, he gave them the Dieselworks' decorations too the next day, as he and the other diesels considered Sidney to be a good enough decoration.
Diesel 10 is an evil, conniving, manipulative, bullying, and raving diesel locomotive. He absolutely despises steam engines, and would call them taunting names like "Puffball" and "Teapot". He is Sodor's strongest but not quite largest diesel, his power being enforced by his slightly malfunctioning claw, Pinchy. He can use this deftly, and is even able to use it to make a sculpture. Pinchy, though, seems to have a mind of its own, as it has been shown to "punch" Diesel 10 in the face from time to time, which he loathes. All engines, steam and diesel alike, fear and respect him.
Despite his brutality, he will help sometimes since Sir Topham Hatt brought him back, but only when it suits his personal interest.
Diesel 10 is based on a BR Class 42 diesel-hydraulic with an added non-regulation hydraulic claw. All but two members of the class were named after Royal Navy warships, so they, and the similar Class 43, were nicknamed "Warships". Two of these engines are preserved.
Diesel 10 is painted ochre with tan stripes along his sides. His buffers and "Pinchy" are painted dark brown.