Iron Bert, along with his twin brother Iron 'Arry, is a diesel engine that works down in the scrap yards and smelters sheds. Iron Bert loves breaking up old steam engines, and would really like to melt down Stepney and Oliver if given the chance. 
In the 15th season, 'Arry and Bert planned to set the Steamworks on fire but the pair accidently lit Percy on fire and Thomas went to get Flynn the fire engine for help. Bert later tried to bam Percy from Sodor but he ran out of fuel whilst on the way to a job. 'Arry then told Bert that Thomas had a new friend named Hiro and they both came up with a devious plan to get rid of Hiro so the pair set off to the place where Thomas had found him when they got there they hid behind some bushes and watched Thomas and Hiro puff away 'Arry and Bert soon got their chance to get rid of Hiro. When Bert and 'Arry returned to the Dieselworks, they saw Dash the Logging Loco with Paxton, Den and Dart and they knew that they needed to come up with a plan to send Dash away forever. 'Arry and Bert are devious twins.
'Arry and Bert are unquestionably devious and scheming. Although at first they had a heartened dislike for steam engines, they appear to have grown accustomed to their smoke-puffing companions.