The Railway Series, which began in the 1940s, is a series of books written by the Rev W Awdry. The books formed the basis for the Thomas the Tank Engine TV series. The Rev Awdry wrote 26 books, pretty much one a year. Later, additions were written by the Reverend's son, Christopher.
The books contain examples of :
Achilles in His Tent: The Sad Story of Henry. Gordon, James and Henry try to invoke it in Troublesome Engines, but it backfires on them.
Thomas becomes a bit stuck-up after he gets his branchline.
Percy becomes arrogant after braving the stormy weather.
Oliver becomes flattered of the remarks of the other engines about his escape from scrap.
All There in the Manual: The books The Island of Sodor: Its People, History and Railways, Sodor: Reading Between the Lines and The Thomas the Tank Engine Man explain between them pretty much everything about the series. What's amazing is how much history there is, from the formation of Sudric kingdoms all the way up to the modern era.
Art Evolution: Mostly due to differing illustrators. The timeline shows Reginald Dalby (1945-1956) as rather childish and miniature, John Kenney (1957-1962) as more realistic and painting-like, Peter and Gunvor Edwards (1963-1972) as impressionistic but like it happened in real life and Clive Spong (1983-present) as about as picturesque as Kenney.
Author Avatar: The Thin Clergyman in the original book series was Awdry, with another railway buff friend, The Rev Teddy Boston, as the Fat Clergyman.
Barsetshire: The whole fictional setting of the Island of Sodor (which is supposed to be just west of the Cumbrian and Lancastrian coast and to the east of the Isle of Man).
Breakout Character: Thomas was a popular character after Book 2, but was only the focus of a few books before the TV series.
Break the Haughty: Happens to a lot of engines. Gordon, James, and Thomas are common examples.
Cast Herd: the standard gauge and branch lines, Skarloey engines, the Culdee Fell engines, the Small railway engines etc.
Continuity Snarl: The story of Godred, an arrogant mountain engine who violently derailed and was subsequently cannibalized for parts (based off of the real world story of Ladas), is a rather confusing affair. The original book, Mountain Engines states that Culdee made the entire story up to scare Sir Handel and Duncan. Yet the various companion books treat the entire incident as a fact, as evidenced by the lack of a No. 1 engine on the CFR. It's further confounded by some of the tie-in magazine stories, which have Godred alive and well, completely recovered from the accident.
Darker and Edgier: Book 13, Duck and the Diesel Engine, began to introduce the concept of Diesels and their takeover of steam, symbolizing that all was not well on Sodor. Further books such as The Twin Engines and Stepney the Bluebell Engine continued this story by introducing scrapping. Enterprising Engines, considered the darkest of all the stories, brought to light the end of Steam elsewhere but on Sodor. Following books, however, got back to the happy adventures.
"He had six small wheels, a short stumpy funnel, a short stumpy boiler and a short stumpy dome."
Determinator: A popular plot thread. Skarloey in Old Faithful, Rheneas in Gallant Old Engine, Edward in Edward's Exploit, Bertie in Bertie's Chase, Percy in Percy's Promise...
Used by the steam engines in arguments with diesels: they may not be efficient or modern, but they get the job done.
Doesn't Trust Those Guys: Gordon tells the others in "Domeless Engines" to "never trust domeless engines; they're not respectable." Guess what happens to Gordon.
Dress Code: Unlike the TV series. The NWR livery is blue, with red lining. Edward, Gordon and Thomas remained this colour, but the other characters were repainted into their trademark unique colours shortly into the series. The Skarloey railway is red, and the Culdee Fell engines purple.
Earlybird Cameo: In later editions of The Three Railway Engines, the engine who tries to push Henry out of the tunnel bears a striking likeness to James.
The engine was actually intended to be James, but when fans pointed out the Series Continuity Error (James' first day was in "Thomas The Tank Engine" where he was painted black), Awdry retconned the engine into a separate character (given several names by fans, including Eagle, Simon, David, and Winston).
Enemy Mine: The trucks cooperate with Percy when it means shutting up Bulstrode the barge.
In a more positive example, writing "Edward, Gordon, and Henry" (the story that establishes said engines as all being on the same railway and gets Henry out of the tunnel) was the condition the publishers set before the Reverend for getting the original book, "The Three Railway Engines" published.
Fantastic Racism: The steam and diesel engines began resembling this, but it died down after some friendly diesels joined the railway. Taken to its extreme in James and the Diesel Engines, in which James is the only engine to still hold a grudge.
Fantasy World Map: The Reverend and his brother spent a good ten years mapping out the Island of Sodor.
Feud Episode: The quarrel between Thomas and Percy in "More About Thomas The Tank Engine".
Franchise Zombie: The Reverend wanted to end the series with Book 12, The Eight Famous Engines, but the publishers wanted the series to continue. He stopped officially after Book 26 for fear of this.
Have a Gay Old Time: In "Thomas and the Breakdown Train", the Breakdown Train contains "two queer things his Driver called cranes." In "Ballast", Duck passes under a chute, on top of which stand "some queer-looking trucks".
Idiosyncratic Episode Naming: Each of the first 31 installments included the word "engine(s)" in the title. The tradition was finally broken with Toby, Trucks and Trouble, although it does show up again a few times afterwards.
I Have Many Names: The Fat Controller in particular has also been called "The Fat Director," "Sir Topham Hatt" and "The Stout Gentleman."
Kick the Son of a Bitch: The troublesome trucks often play tricks on an engine who were being mean or arrogant to others (i.e., James in "Dirty Objects" and Diesel in "Pop Goes The Diesel".
Laser-Guided Karma: This occurs at almost every single time. Whenever there's an engine who is being either rude, haughty, or stubborn, they will get themselves into an unfortunate mishap or accident, not to mention they will receive ridicule from the other engines. This often causes the engine to become nicer and wise enough to not make the same mistakes again.
Lazy Artist: C. Reginald Dalby. He could have easily gone down to the station near his house to see real engines to base his illustrations on, or he could have looked at photographs, but he didn't. He couldn't be bothered to be keep engines' proportions consistent (resulting in Percy eventually looking like, as Awdry put it, "a green caterpillar with red stripes") or even keep track of how many wheels he drew Henry with. This was the reason for Henry's rebuild - Awdry had to have him rebuilt as a specific real class of locomotive so that he could send Dalby reference photos.
Long Runner: Book 1 was published in 1945, Book 42 was published in 2011.
Malicious Slander: Diesel uses this to try and get rid of Duck. Gordon, Henry and James are fooled, but not the Fat Controller, and Diesel ends up exposed and sent packing when he tries to slander Henry.
Never My Fault: The Engines being blamed for Human error. A common example includes Thomas being blamed for crashing into the stationmaster's house even though it was a cleaner that carelessly fiddled with his controls.
No Sympathy: This happens quite a lot. Whenever there's an engine who laments about their unpleasant situations, this will lead them to get teased. However, this mistreatment on the engine depends either if the engine receiving this treatment had brought it upon themselves due to their misbehavior, or that the engine expressing their lack of sympathy to another was being rude for their own sake, in which case something will likely lead them to get A Taste Of Their Own Medicine shortly afterwards.
Henry received this treatment from the engines following his increasing illness. Other engines usually ignoring his moaning until he starts effecting their own work schedule (Thomas in particular chewed out Henry for making him late, and only saw his ill bout as an opportunity to pull his train in his place). Only his crew and Sir Topham Hatt shown concern for his health and took measures to repair him, leading him to get the last laugh on some of the apathetic engines from before when he starts to outclass them.
Real Life Writes the Plot: Skarloey Railway locomotives sometimes visit the Talyllyn Railway, a move designed to write in the fact that Talyllyn locomotives are sometimes decorated to look like their Skarloey counterparts
Recurring Extra: The Works Diesel, a BR Class 47 who has appeared, unnamed, since Book 28, but is described by the other engines as friendly.
Sequel Hook: The Fat Controller says in Wilbert the Forest Engine that if Wilbert performs well, he knows where to find another engine like him.
Shout-Out: The Non-Standard-Gauge railways on Sodor are based on real life ones. The Skarloey railway is based on the Tallylln railway, the small railway is based on the Ravenglass and Eskdale Railway and the Culdee Fell is based on the Snowdon mountain railway.
The title for Thomas And His Friends was most likely a shout out to the television series.
The fireman who got annoyed at Henry for spilling his hot chocolate instead of crashing into the back of the Brake Van and almost killing him.
The Painter that got angry at Henry for spilling his paint rather then making him lose his balance on the ladder.
The Barber that got angry with Duck for frightening his customers rather then crashing into the Barber shop which may of endangered the lives of said customers.
The Signalman that got annoyed with Donald for jamming his points and not endangering his life.
The Station Master's wife who chewed out Thomas for ruining her and her family's breakfast instead of crashing into the house and endangering the life of her family.
Small Name, Big Ego: A recurring character trait for several engines, but particularly Gordon, James and Sir Handel. Thomas also became one though was eventually toned down a little under Christopher Awdry's pen.
Space Whale Aesop: Don't be reckless or put yourself into dangerous situations or you might have your body parts used to heal your sick friends.
Steam Never Dies: Not on Sodor, at any rate. Due to the degree of operating independence given to the North Western Railway under British Rail the mass-dieselization order did not apply, and since the railway is still turning a decent profit after Privatization the Fat Controller sees no reason to change things - especially given the years of hard work the engines have all put in.
Take That: In one story, Thomas refers to Percy as a "green caterpillar with red stripes". This was the exact wording that the Reverend used when he reacted poorly to earlier illustrations of Percy by Reginald Dalby. Dalby didn't take it too well.
Twin Switch: Donald and Douglas in The Missing Coach, Bill and Ben in The Diseasel.
Unusually Uninteresting Sight: Many people's reactions to engines causing destruction and havoc are extremely tranquil. Take this underwhelming reaction from a barber after Duck crashes into his shop: