In their first appearance, 'Arry and Bert crept alongside a lonely Stepney, who had mysteriously been sent to the scrapyards by mistake. They shunted Stepney into the larger smelting shed underneath a giant grabber, and threatened to scrap him. Thankfully, Stepney was saved by Sir Topham Hatt, once the diesels had left.
Despite being villainous, 'Arry and Bert are also known for playing tricks on steam engines, such as making them "middle engines". Once, they shunted trucks in front and behind Percy. This later lead Percy to being pushed onto the coal tipper by mistake. Later, 'Arry and Bert played the same trick on James. Sometime later, they frighted Fergus away from the smelters, and made the engines believe Neville was planning to bump them.
On some occasions, 'Arry and Bert's teasing ways backfire. Once, they played a ghostly prank on Thomas and Emily during Halloween, though they ran away when they thought Emily was a ghost. Another time, 'Arry and Bert teased Percy for having a whistle. Percy payed them back by creeping up behind them and blowing on his whistle. Later, Diesel, 'Arry, and Bert began teasing Thomas for being smelly, but were later covered in stinky cheese.
'Arry and Bert were also part of the group of Diesels that took over the Sodor Steamworks. They later teased Henry because of the coal he had to use by calling him "Mr. Special Steam".
They also laughed at Gordon after he ran into Diesel's flatbed and damaged his bufferbeam.
In the twentieth season, 'Arry and Bert liked being rough and tough along with Diesel, they realised Diesel was trying to be nice to everyone. So Thomas took 'Arry and Bert to the ducklings while Diesel followed behind them. Diesel, 'Arry and Bert then realised the ducklings were cute.
'Arry and Bert are unquestionably devious and scheming. They feel superior to steam engines and, working at the scrap yards, they enjoy the chance to break up engines, or at least make their lives more difficult. Due to their grim task, they have earned a reputation on Sodor as "The Grim Messengers of Doom." However, despite their prejudices, the diesels have co-operated with steam engines on occasions, and when they are in trouble, steam engines often come to the rescue.
Despite being villainous, 'Arry and Bert also have a tendency to act scheming, slimy, greasy, and oozy. 'Arry is usually shown to be the leader of the two, while Bert carries out most of the orders. According to their merchandise bios, they wish to scrap Oliver and Stepney, whom have escaped the cutting torch once before.
- Arry and Bert will make their first guest starring appearance in Thomas' Adventures of Looney Tunes: Back in Action.
- Arry and Bert are also best friends with Diamond Tiara and Silver Spoon.