In their first appearance, 'Arry and Bert crept alongside a lonely Stepney, who had mysteriously been sent to the smelters 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 frightened Fergus away from the smelters, and bullied Neville, which made the engines think he 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, Harry and Bert teased Percy for having a whistle. Percy payed them back by creeping up behind them and blowing on his whistle. Later, along with Diesel, Harry, 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 realized 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 realized 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. According to their merchandise bios, they wish to scrap Oliver and Stepney, whom have escaped the cutting torch once before.
'Arry and Bert are BR Class 08 shunters. Over seventy members of this class survive today in preservation. Diesel, The Diesel Shunter, Splatter, Dodge, Paxton, and Sidney are also members of this class.
'Arry and Bert are painted green-grey with yellow hazard stripes on their fronts and rears with yellow cabs. They have "Sodor Ironworks" written on their sides in white.
- Kerry Shale (UK/US (fourteenth season onwards))
- Kerry Shale (UK/US (fourteenth and fifteenth seasons))
- William Hope (UK/US (sixteenth season onwards))
- The two are not quite identical: Bert has more stubble.
- In some merchandising, the twins are named "Iron 'Arry" and "Iron Bert".
- Harry and Bert's television series models do not have handrails, although some of their merchandise lines do.
- The 1998 Official Website and Question Time with Sir Topham Hatt called Harry and Bert "The Yellow Diesels".
- Harry and Bert's fifth season models were repainted and constructed into Splatter and Dodge for Thomas and the Magic Railroad.
- A model of Harry and 1 of Bert used to be on display in Canada at Nitrogen Studios.
- Harry's name was not revealed until merchandising of him was released.
- Harry and Bert have gone through a few changes in the television series:
- Season 6
- Their side rods change from silver to black.
- Their faces became smaller.
- The text, "Sodor Ironworks", on their sides became bigger.
- Their models were significantly less weathered than the previous season.
- Season 12
- Their faces become smaller still.
- Season 14
- Their faces returned to the size they were in Season 5.
- Season 6
- On their trading cards and Bachmann models, Harry is depicted with more stubble than Bert, opposite of how they usually are.
- In all of their appearances in the eighteenth and nineteenth seasons, 'Arry and Bert's faces were obscured from sight
- ERTL (discontinued)
- Wooden Railway (normal, oil-covered (discontinued (cheese-covered Bert (discontinued))))
- Take Along (normal and metallic (discontinued))
- Hornby (discontinued)
- Lionel (discontinued, later reintroduced with LionChief remote)
- Capsule Plarail
- My First Thomas
- My Thomas Story Library (discontinued)
- Trading Cards (discontinued)
- De Agostini (discontinued)
- Minis (Harry - DC Super Friends (Bert - classic, neon and electrified))