Thomas is the number 1 engine on the North Western Railway. He runs a branchline, together with hiscoaches Annie & Carabel and another tank engine, Ryan.
Thomas was present at the VE Day celebration at Maron Park when a strange car came and towed the statue of King Maron away. He later asked the Fat Controller what any of this means, to which he is informed of the story of King Maron and King Godred.
Thomas had his picture taken for a billboard, and later gloated to Diesel about it. When Diesel asks why he hadn't been chosen, Thomas replies that he is a diesel, and that Sir Topham wants to showcase his steam engines.
When Sir Topham Hatt was planning a retaliation against Percival, Thomas was chosen to undertake the "special task".
Thomas was working on his branch line when he saw Spencer quickly approaching. He was forced to stop suddenly, causing him to derail. While at the Steamworks getting repaired, he and Spencer discussed the suspicious nature of the latter's accident.
Thomas was pulling Annie & Clarabel near the yards when he was stopped and asked to go to the Scrapyards to collect a part. Despite his reluctance, Thomas is eventually persuaded. Before he leaves, he angrily tells Diesel off for failing to fulfill his duty. While at the Scrapyards, he is cornered by 'Arry and Bert, who threaten him with scrapping. He spots Diesel looking on, begging him to save him. When Diesel leaves, he further becomes discouraged. He is rescued however when Diesel returns with Sir Topham Hatt, who calls the diesels off. Thomas later apologizes to Diesel, who forgives him for his misdeeds of before. A few days later, Thomas invites Diesel to Tidmouth Sheds to spend the evening with the other engines out of gratitude. However unknown to the little tank engine, while the engines were celebrating the breakdown of the Duke and Duchess' new diesel, (Derek) Diesel arrives only to overhear the engine's conversation and sadly left.
Turtlesandthomas used many different models of Thomas throughout the series for different emotions such as shocked and miserable, and use the older model of Thomas for flashback episodes.
When Thomas first arrived he was very inexperienced but through trial and error and the rescue of James he learned the ropes of Sodor. Years later Thomas became a very calm friendly engine but can be seen to be very prejudice such as when he referred to diesel as an olier. This trait did not last as Thomas soon accepted diesel and even gave a speech to the other engines to not be so cruel to Diesel.
- Season 1: Sodor Day, Tensions Emerge, False Retaliation, Duke & Duchess, Justified Retaliation, Revolutionary, The Final Solution, Hatt
- Season 2: Consequences, Reform, The UK Trip, Authority
- Season 3: Inheritance Parts 1, 2, 5, 6 and 7