Thomas the Tank Engine is one of the most beloved fictional characters in both the UK and the US. A sentient blue locomotive, he lives on the island of Sodor with other trains. Together, they work to haul cargo and passengers to and from various locations. However, while there is an apparent innocence to the decades-old character, there's also a theory that paints a dark picture about what is really going on on the island of Sodor.
A theory that has gained traction over the years posits that the trains on the island are slaves to the island's leader, Sir Topham Hatt/The Fat Controller. According to the theory, these trains are forced to work for the Fat Controller, and if any of them get out of line, they are sentenced to a fate similar to death. To add even more credence to the grim theory, the hit television show also displays this action in one of its many episodes.
In "The Sad Story of Henry," one locomotive, Henry, is too scared to go out in the rain. He hides in a tunnel and refuses to keep moving until he's sure the rain won't return. Outraged at his insubordination, the Fat Controller takes away Henry's tracks and bricks up the tunnel just enough for him to see out of. Effectively, the Fat Controller sentences Henry to an eternity in the tunnel until he rusts away or perishes. Even worse, this fate is only because the train had no interest in moving.
Whether captured to work on the island or not has never been revealed, but the concept of brainwashing has also been tossed around. There's even potential evidence to this in the same episode that Henry is walled up, as other trains roll by spouting comments like, "Serves you right!" Logically, a punishment like this doesn't fit the crime, and that type of comment only shows that these trains could be conditioned to think that going against the rules is wrong on Sodor.
Like the droids in Star Wars, trains are treated more like a utility than an individual. While they don't have traditional bodies, they can still think for themselves. As a result, they should get the same respect as the people, but an extended aspect to the theory may explain why the humans are so focused on the trains staying in their lane. According to a Sun article, the trains are enslaved because Sodor is the only island with life, and an apocalypse has ravaged the world around it. While there's no evidence to prove the claim, it does explain the importance that everything runs smoothly to avoid another catastrophe.
Whether or not the Fat Controller's tyrannical rule over the trains is true remains to be seen. However, it does offer a context for moments like what happened to Henry and why his actions earned him such brutal punishment. That said, in a series that teaches young viewers life lessons like facing their fears and overcoming obstacles, it could help explain why the Fat Controller acted so rashly to an act so innocent.