Mr. Peregrine Percival, nicknamed "the Thin Controller" ("Narrow-Gauge Controller" in the US), is the current manager of the Skarloey and Culdee Fell Railways in the television series. In the magazines, he also runs a Cable Railway.
Mr. Percival was hired sometime between the seventh and ninth seasons to help Sir Topham Hatt 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 Sir Topham Hatt, called for help when the Duke and Duchess of Boxford needed to get to Callan Castle and he attended Sir Robert Norramby's Christmas Luncheon.
- Keith Wickham (UK; sixteenth season onwards)
- Kerry Shale (US; sixteenth season onwards - NZ; Duncan and the Grumpy Passenger only)
- 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's Take-Along and Take-n-Play models both feature him inside of a car, whereas he has only ever been seen with a bicycle.
- From the ninth to the eleventh seasons, the top of Mr. Percival's head was bald. However, since the cross over to CGI in the twelfth season, he has a full head of hair.
- 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.
- Wooden Railway (discontinued)
- Take Along (in red car; discontinued)
- Take-n-Play (in red car; discontinued)
- TrackMaster (with Fearless Freddie in "Ding a Ling"; discontinued)