Before the conflict of 1945, Andy had came to the North Western Railway as a temporary replacement for Henry who had been sent to Crewe to be rebuilted after his accident with the Flying Kipper, upon his arrival he insulted the steam engines, before heading into Henry's shed to rest after his long journey from the mainland. The next morning Andy was scheduled to pull a passenger train, but broke down much to the steam engines amusment and Andy's embarrassment. He was shunted back into the shed and Duck went to pull the train, Andy was so embarrassed, that he had his shed door closed leaving only two things behind, a rather dreadful smell, and a battered bowler hat.
Spring soon came to Sodor, bringing the new engines, Lady and Diesel, who Andy was talking to about how steam engines were treated, and how diesels didn't get the same attention. Diesel tells Andy that Lady is polite and kind, while he was a shunter, who doesn't expect admiratio before heading off to finish his work. Several weeks later, there was a really bad storm, leaving broken branches scattered everywhere. So Sir Topham Hatt tells the engines that he bought a diesel with a hydrolic claw to help him pick up the branches.
When Diesel 10 arrived, Andy was the first to greet him, when Diesel 10 asked him his name, it made him even more happy as it was the first time anyone has asked him his name ever since he came to Sodor, after introducing himself, he finds out that Diesel 10 hadn't been given a proper name, he decided to call him "Pinchy" after Diesel 10's claw. Over the next few weeks the two became close friends, upon learning that 10 was due back in Ireland, the Diesel came up with a plan and told it to the Warship. As Andy was due in The Quarry in a few hours, he planned to fake some engine troubles so Lady would go in his place, and then Diesel 10 would follow her, and whatever would happen, happen.
That night right on que Andy mysteriously broke down and Hatt sent Lady as planned. And while Lady was working, she didn't hear 10 purring up behind her and using Pinchy, Diesel 10 grabbed a hold of her backless cab and throwing her off the cliff and into the ocean below. Unfortunately for Diesel 10, Lars had seen the whole thing and told Sir Topham the following morning, and came to see Andy and Diesel 10, and asked Andy if he could talk with 10 in private. When Andy asked what Hatt had said to him, Diesel 10 told his friend that he had been found out, and was going to be sent away the next day. After he left, Andy found himself alone on Sodor once more, he tried talking to Diesel, Mavis, and BoCo to start a diesel revolution, but wasn't successful, then one day in July, he was told that Henry was due to return soon, and was no longer needed. Andy Diesel left the Island of Sodor feeling that he failed to accomplish his goals. When he returned to the mainland he was locked up in his shed for nine years, planning his revenge on the Railway.
After Sir Topham Hatt and Mr. Percival died, and Alfred Herman took control of Sodor, Andy returned along with Diesel 10 and a whole bunch of new diesels bought from Rudolph Diesel, but arrived later at night. At first Diesel 10 didn't recognize him, until Andy said his nickname, 10 instantly recognized him. Andy tells him, that he had big plans for Sodor and needed his help to carry them out.
When Diesel 10 tried to convince the other diesels not to trust the steam engines, they remained doubtful weather to believe him or no, until Andy told them all the story of how he first came to Sodor, which did the trick and resulted in the formation of the Oiler Committee. After watching Alfred Herman and the workmen leaving on a ship to the mainland, he rallied the other diesels into taking over the Sodor Steamworks, and kicking Victor out of the Steamworks. When Gordon went to investigate, Andy violently shoved him out of the Steamworks, claiming it was theirs now. After Toby's death, Percy went to confront Andy, asking him if he was Mr. M, which results in Andy giving a haunting speech of the future of steam engines to the little green engine. When Diesel, BoCo, and Mavis went into the Steamworks, Simon Johnson went into the building to meet Andy, and both finding out they both had a lot in common and decided to be partners, and continued with causing much more destruction on Sodor, and kidnapping and scrapping Edward, this was then when Diesel learned what really happened at the Sodor Dieselworks, causing him to switch sides to the steam engines. When D199 told Andy that the steam engines had left Tidmouth Sheds and went to the Skarloey Railway to seek refuge with the little Engines, he went to check to make sure it was true.
When Diesel 10 told Andy that he had found Lady's remains at The Docks, it gives Andy an idea. They both soon take Lady to the Transfer Yards, and presented it to Duke telling him it would soon happen to them, this makes the old engine furious and orders them to leave and tells them to leave him and his friends alone, and the two do so, but return and capture Duke in the night, but beforehand Diesel 10 and Andy advanced on BoCo and Mavis, when they wanted out of the Oiler Committee, which they didn't take lightly, while 10 ripped Mavis' side plates, BoCo escaped from The Scrapyards.
A few days later, Andy had come up with another plan for scrapping the steamers, by having Diesel 10 and Spamcan kidnap Percy, and taking him up to the quarry, which made Thomas and Gordon go looking for him, when they encounter Splatter who was placed by Andy to pretend that he had betrayed Andy and the other diesels. When Thomas and Gordon arrive at the top of the quarry, they realize too late that it is a trap, and Gordon was captured and scrapped, leaving the two tank engines to watch as their friend was dragged away.
When Thomas and Phil Aardman tried to escape the quarry, Thomas runs out of water and was captured by Diesel 10, and taken to the scrap yards, this pleases Andy as once they got rid of Thomas, he would become the new number one of Sodor, when Phil asked Andy who Mr. M was, Andy revealed that the diesels and Mr. M were working together, before he had Simon take Phil away.
In the events of "Authority" Andy had made another plan to get rid of the remaining steam engines once and for all, by having Mr. M strap a pressure activated bomb to Dodge's engine, while Phil was being chased by Simon, the two could be seen heading towards the Skarloey Railway. Once they reach McColl Farm, Dodge asks him what the plan was, Andy frustrated, reminds him of the bomb, and to have him charge at the steam engines and crashing into the back of one, and the bomb would activate destroying the steam engines, claming it would bring change and reform, and the modernization era for Sodor. However unknown to them, while Dodge was trying to get out of being a suicide bomber, Diesel had overheard them. Realizing he had to save the steam engines, Diesel charged into Dodge, causing all three to be blown to smithereens, ending Andy's rain of horror once and for all.
It is unknown if his and Dodge's remains were used with Diesel, Lady, Edward, and Gordon's remains were made into the statue of Diesel for Maron Park.
Andy Diesel is based on the character with the same name from leokimvideo's Mad Bomber Video as a tribute to him.
Andy's deceased body was used from a Take-N-Play Class 40 Model with it's face removed and heavily weathered.