Mr. Peregrine Percival, also called the "Thin Controller" ("Narrow-Gauge Controller") in the US), is the current manager of the Skarloey Railway
Mr. Percival was hired sometime between the seventh and ninth seasons to help The Fat Controller manage the ever-increasing size of the railway industry on the Island of Sodor.
Mr. Percival is married to Mrs. Percival and has five children.
He was one of the important visitors who attended Dowager Hatt's special tour of Sodor and then a party at Knapford. He later charged Peter Sam with the running of the Skarloey Railway whilst he attended a meeting with Sir Topham Hatt, and welcomed Luke to his railway.
He scolded Duncan for his grumpy disposition at Christmas time. He told Duncan that he had to be cheerful all day, but later realised that demand was too hard for the grumpy engine.
He later attended a meeting with The Fat Controller, called for help when the Duke and Duchess of Boxford needed to get to Callan Castle and attended Sir Robert Norramby's Christmas Luncheon.
Mr. Percival appears to be acquainted with the Thin Clergyman, as he was seen speaking to him at Vicarstown and also watched the events of the Great Railway Show with him.
- Season 2 - Rheneas' Risky Ride, Trouble on the Line, Fred Goes on Strike, and Flying Scotsman Departs (cameo)
- Season 3 - The New Controller (cameo), Fearless Fred, Duncan's Discovery, and Bertram and the Christmas Party
- Season 4 - Duncan and Victor (mentioned)
- Season 5 - Smoke Signals
- Season 6 - James and the Royal Train (cameo)
- Due to political correctness in the US, he is known exclusively as Mr. Percival, whereas he is known as the Thin Controller in the UK. Sir Topham Hatt (aka The Fat Controller) has the same issue.
- Mr. Percival wears visually similar attire, with corresponding colours, to the television series Fat Controller's clothes, except he wears a bowler hat instead of a top hat and has a regular suit jacket instead of a tail coat.
- Mr. Percival is often accompanied by a workman holding his bicycle.