Pygmalion

Pygmalion (full title: Pygmalion: A Romance in Five Acts) is a 1913 play by George Bernard Shaw.

We open on a crowd sheltering from the rain in a church porch. Among them are an impoverished aristocratic mother and daughter, the Eynsford-Hills (who dispatch Freddy, the son of the house, to secure them a cab); Colonel Pickering, a student of Indian dialects; and Professor Henry Higgins, a professional linguist. These are joined by Eliza Doolittle, a Cockney flower-girl (nearly knocked over by the departing Freddy), whom Higgins repeatedly startles, first by taking down her speech in phonetic writing, then by declaring to Pickering (whom he has invited to his home) that he could teach her to speak proper English, and finally by presenting her with a great deal of money -- which she uses to commandeer the taxi which the feckless Freddy has brought for his already departed family.

Eliza, inspired by Higgins' boast, comes to his house for lessons. Pickering makes a wager with Higgins, that the latter must in six months' time pass Eliza off as an aristocrat at an Embassy Ball. To effect this, Higgins bullies and wheedles Eliza into remaining at his home. Eliza's dustman father, Alfred Doolittle, gets wind of this and comes to extort money out of Higgins -- which Higgins, delighted by Doolittle's charmingly amoral manner, gladly gives him. Eliza's lessons duly proceed.

Sometime later, Higgins brings Eliza to his mother's At Home day to try her out on Society; Mrs. Higgins' guests just happen to be the Eynsford-Hills. Eliza's conversation, though conducted in a properly aristocratic accent, is thoroughly low-class in grammar and content. Hilarity Ensues, as Eliza departs with a shocking vulgarism, leaving Freddy frankly in love with her and his sister determined to emulate Eliza's elegant "small talk." Higgins' mother remonstrates with him, to no avail.

Months later at the ball, Higgins and Pickering present Eliza to the scrutiny of the venal language expert, Nepomuck, who has been charged by the hostess with detecting any social frauds. Because of his language expertise, Pickering is certain that Eliza will be seen right through. Nepomuck thoroughly deceives himself, however, identifying Eliza not only as an aristocrat, but as a foreigner as well; even when Higgins himself identifies her as a Cockney commoner, his Cassandra Truth is not believed.

With the ball over -- What now? Eliza's new character has unfitted her to be a flower-girl, and left her financially unable to maintain her character as a lady. The rest you'll have to see yourself. (And even that might not answer your questions, so you may have to read the "Afterward" Shaw appended to the play after he first wrote it.)

A well-received film version was shot in 1938, with Shaw winning an Oscar for his script.

It created the modern Pygmalion Plot and directly inspired My Fair Lady.

Tropes used in Pygmalion include:

Ambiguously Gay: Pickering.
Beautiful All Along: Eliza.
The Bet
Boy Meets Girl
Crash Into Hello: Freddy and Eliza
Dawson Casting: A particularly ridiculous case: the original Eliza, Mrs. Patrick Campbell, was forty-nine when she created the role.
Deadpan Snarker: Henry Higgins, and then some.
Deconstruction: The "Pygmalion Plot" was actually very common in the day before this. This actually shows what's wrong with The Makeover.
Funetik Aksent: Shaw attempts to do this to represent Eliza's speech at first, but abandons it as unintelligible. (Throughout, however, he refuses to make use of standard English orthography, especially for contractions.)

THE FLOWER GIRL. Ow, eez ye-ooa san, is e? Wal, fewd dan y' de-ooty bawmz a mather should, eed now bettern to spawl a pore gel's flahrzn than ran awy athaht pyin. Will ye-oo py me f'them?

GPS Evidence: Henry Higgins can determine a Londoner's address down to the street name by his accent alone.
Grammar Nazi: Higgins is more of a diction Nazi, but An Aesop about judging people by the way they speak still applies.
Have a Gay Old Time: Nepomuck is nicknamed "Hairy-Faced Dick."
Ironic Echo: "Oh, I'm only a squashed cabbage leaf!"
Ironic Name: The language expert Nepomuck is named after a Bohemian saint famous for being martyred for refusing to divulge the secrets of the confessional.
Jerkass: Henry Higgins.
Lighter and Softer: Compared to his other plays. Shaw usually upheld the idea that Some Anvils Need to Be Dropped, but, by popular demand, Pygmalion has a relatively light and humorous tone compared to Mrs Warren's Profession and Man And Superman, both of which can seem downright brutal.
Man Child: Higgins is portrayed as being very childish -- mischievous, manipulative, candid, sulky, ill-mannered, selfish, tyrannical, thoughtless and a complete mamma's boy (much to the dismay of said mamma). He's even described as being like a baby or a child repeatedly by the play's direction and occasionally by his mother. Pickering is this to a lesser extent.
Momma's Boy: Henry Higgins (!)

Higgins (to his mother): "My idea of a lovable woman is something as like you as possible."

Platonic Life Partners: Eliza and Henry Higgins, as George Bernard Shaw insisted.
- Worth noting, people have been thinking JBS was full of it from day one. Even the leads in the original production (who would take their bows posed side-by-side like a bride and groom).
Precision F-Strike: An accidental one, but it has the same effect.

Freddy: Excuse me, Miss Doolittle, would you be walking across the park, cause if so I--
Eliza: Walk? Not bloody likely. I'm going in a taxi.

Pygmalion Plot: The Trope Maker
Red Oni, Blue Oni: Henry Higgins and Colonel Pickering, to a degree.
Self-Insert Fic: Higgins is based to some extent on Shaw himself, and his relationship to Eliza echoes Shaw's with the actress Sybil Thorndike.
She Cleans Up Nicely: Eliza at the ball.
Ship Sinking: The Afterword explains why a particular pairing wouldn't work well.
T-Word Euphemism: Mrs. Pearce reprimands Professor Higgins for setting a bad example to Eliza:

Mrs. Pearce: "...but there is a certain word I must ask you not to use. The girl has just used it herself because the bath was too hot. It begins with the same letter as bath. She knows no better: she learnt it at her mother's knee. But she must not hear it from your lips."