Stephen Topham Hatt (born 1941) is Sir Topham and Lady Hatt's grandson and Bridget's older brother. In the Railway Series, he took over his father's role as controller of the North Western Railway in 1984 and became Sir Topham Hatt III in 1997.
He later appeared in the following books as the Fat Controller:
- Season 1 - Thomas and Gordon (cameo) and Toby and the Stout Gentleman
- Season 2 - Old Iron (cameo) and Wrong Road (cameo)
- Season 3 - Percy's Promise (cameo), Time for Trouble, Thomas Gets Bumped (cameo), and Edward, Trevor and the Really Useful Party (cameo)
- Season 4 - Peter Sam and the Refreshment Lady (cameo), Steam Roller (cameo), Bowled Out (cameo), and Bulls Eyes (cameo)
- Season 5 - A Better View for Gordon (cameo), Bye George! (cameo), Baa!, Toby's Discovery, Something in the Air (cameo), and Sir Topham Hatt's Holiday
- Season 6 - Harvey to the Rescue (cameo), No Sleep for Cranky (cameo), James and the Red Balloon (cameo), Thomas, Percy and the Squeak (cameo), and Edward the Very Useful Engine
- Season 7 - Snow Engine, Rheneas and the Roller Coaster (cameo), Harold and the Flying Horse (cameo), and Three Cheers for Thomas (cameo)
- Season 8 - Thomas and the Tuba (cameo), Henry and the Wishing Tree (cameo), Thomas Saves the Day (cameo), Thomas and the Firework Display (cameo), Squeak, Rattle and Roll (cameo), Thomas and the Circus (cameo), Chickens to School (cameo), and James Goes Too Far (cameo)
- Season 9 - Thomas and the Birthday Picnic (cameo), Percy and the Oil Painting (cameo), and Thomas Tries His Best (cameo)
- Season 10 - Follow that Flour (cameo), Thomas and the Jet Plane (cameo), Percy and the Funfair (cameo), Seeing the Sights (cameo), Which Way Now?, Sticky Toffee Thomas (cameo), and Thomas and the Treasure (cameo)
- Season 11 - Thomas and the Storyteller (cameo), Edward and the Mail (cameo), Toby's Triumph (cameo), Thomas and the Runaway Car (cameo), Thomas and the Big Bang (cameo), and Percy and the Left Luggage (cameo)
- Season 13 - Thomas and the Runaway Kite
- Season 14 - Diesel's Special Delivery
- Season 15 - Wonky Whistle (cameo)
- Season 16 - Muddy Matters (cameo)
- Season 17 - Wayward Winston (cameo)
- In the magazine story, The Hallowe'en Special, it is said that Stephen and Bridget live on the Mainland and only come to stay with Sir Topham and Lady Hatt every so often.
- In the magazines, he and Bridget have a friend named Marcus.
Sir Topham and Lady Hatt with Stephen and Bridget
Stephen and Bridget
Stephen, Bridget, Sir Topham, and Lady Hatt
Mavis, Bridget, Marcus, and Stephen