I Can Change My Beloved

"Marge: Well most women will tell you that you're a fool to think you can change a man, but those women are quitters!

Lisa: What?

Marge: When I first met your father, he was loud, crude, and piggish. But I worked hard on him, and now he's a whole new person.

Lisa: Mom...?

Marge: He's a whole... New! Person!"

- The Simpsons, "Lisa's Date With Density"

Alice, a Love Martyr, has a Love Interest who is destructive, or merely "wrong" in some way subjective to the character. Nope, Bob certainly isn't the perfect match, but never fear! Her love will send him through a metamorphosis that will remake him into her perfect man. Or so she thinks. Of course, it rarely works out. If it actually does, then it is Love Redeems rather than this trope. In a long story arc it can be both tropes: First I Can Change My Beloved, then switch to Love Redeems... and then, if the authors are cruel, switch back so that the actual redemption was just a facade or temporary phase.

While there are a lot of male examples, this trope is usually female, and one of the main reasons why All Girls Want Bad Boys. Usually Played for Drama. Sometimes played for Fetish Fuel as a component in Bastard Boyfriend, or, hypothetically (but rarely seen), in its Distaff Counterpart Bastard Girlfriend.

Compare Destructive Romance. Contrast Love Redeems and Reformed Rakes, where this mindset actually works. Also compare/contrast Draco in Leather Pants where this mindset works because the one who has the mentality is the author!

If the specific point of the Love Interest that needs changing is their wardrobe, it's I Want My Beloved to Be Fashionable.

Anime and Manga

 * This is a staple of the Shoujo and Josei mangas where the lead is a Bastard Boyfriend.
 * Infamously used in the ending of the Hot Gimmick manga; our protagonist Hatsumi, despite all evidence to the contrary, decides to marry the Jerkass love interest Ryuuki because maybe she can change him once they're together. (This is true only for the Manga: In the novelization, Hatsumi considers this trope, realizes it's bull, and goes for a slightly less awful love interest instead: Shinogu.)
 * In example, Kurumi Akino from Haou Airen thinks she can pull this in regards to Hakuron, the dude who practically kidnapped her and brought her to Hong Kong to be his mistress. (Then again the poor girl is trapped in the SAR and has no real way out, considering Hakuron is a high-ranked Triads leader.) In any way, it does NOT go well.
 * In Code Geass, Shirley thinks it's her duty to reform Lelouch because he's a "failure as a person". Since she only sees the Brilliant but Lazy Rich Idiot With No Day Job persona he maintains at school, and has no idea what a Magnificent Bastard Anti-Hero he is in his other life, this particular aspect to her romance is either Played for Laughs or for tragic Irony, depending on your viewpoint.

Comics

 * According to Word of God from Bob Kane, the entire point behind the relationship between Batman and Catwoman is that Batman partly thinks he can reform her. And in some continuities (such as Earth-2 of Pre-Crisis), he's actually right.
 * To a lesser extent, this is also true of his other big love, Talia Al Ghul.

Documentary

 * The BBC documentary The Human Animal proposes a reason this trope exists in simple biological terms. The short of it is that the dangerous aspects of the target are sexual advertisements. According to the documentary, on a biological level, women are looking for signs of protective prowess (a partner who will help protect and rear offspring). Displays of aggressive behaviour are then read as signs of this prowess (cultural signs of this vary greatly, but the intended messages are the same). Once partnered up, however, the female will actively work to prevent the male from displaying further (which is this trope), so as to prevent the male from gathering further attention from the opposite sex. There's a lot more to human courtship, of course, mostly because unlike other primates alive today, sex among humans lasts more than 8 seconds.

Film

 * In Spy Kids 2, Carmen had a crush on the rival bad boy spy and at one point insisted she could change him. She appears to get over her crush on him at the end of the movie.
 * In Revenge of the Sith Padme said that Anakin was a good man even though he killed sand people, and even after he had killed children,

Literature

 * In the Sherlock Holmes story Valley of Fear, Ettie falls prey to this. More justified than usual; her beloved starts out as a relatively decent guy with a Dark and Troubled Past (certainly better than the brutish Romantic False Lead she started with), and she fights the influence of the criminals that own their town when they start sucking him in. It actually works out for her, but only because
 * In The Tenant of Wildfell Hall, Helen enters into her marriage with Arthur looking forward to changing and redeeming him, only to find that it's not that easy. She ends up thoroughly miserable, and in fact leaves him (an unspeakable move at the time) to rescue their son from his influence. This is also played straight in the same book: her friend is miserable in her marriage, but her husband is willing to change, and with a few points from both his wife and Helen, he shapes up into a very considerate partner.
 * In PG Wodehouse's Hot Water, Beatrice thinks she can turn Packy into a man of culture. A common trait of certain Wodehouse fiancees - who always turn out to be the wrong woman.
 * In Sweet Myth-Tery of Life Chumley shared his thoughts on marriage, noting common disastrous delusions, including people trying to "marry the person they think their partner will become".

Live Action TV

 * When Charlie's mother met his first serious Love Interest on Two and A Half Men, they squared off like a confrontation was about to take place. Instead, the mother simply asked desperately, "Can you fix him?" Exasperated, the girl confirmed, "I'm trying." True to her word, the entire episode was about her forcing Charlie to give up smoking and drinking, eat healthier, and incorporate exercise into his lifestyle. His Stalker with a Crush tells him that she would never try to change him because she actually loves him. The scenario backfires when Charlie finally takes a stand against his girlfriend- he puts his foot down in a fancy restaurant, getting the male clientele (similarly browbeaten) to back him up. The issue is dropped from then on.
 * An episode of the Adam West Batman series has The Penguin fool a wealthy woman into falling in love with him just so he can earn her trust then rob her. After his scheme is exposed she is still in love and insists if she were to marry him she could reform him into a perfect man. Penguin's response? "Take me to prison!"
 * In Degrassi there are the good girls, "cause girl" Emma and the Christian Darcy who only like bad boys so that they can make them good.

Theater
"Questioner: What do you do when you love someone?
 * "If Mr. Keuner loved someone" by Bertolt Brecht:

Mr. Keuner: I make a sketch of the person, and make sure that one comes to resemble the other.

Questioner: Which, the sketch?

Mr. Keuner: No, the person."


 * The song "Marry the Man Today" ("and change his ways tomorrow!") from Guys and Dolls is all about this, and indeed it seems to work out well enough for Sarah.

Video Games

 * Appears in Neverwinter Nights 2 during the abortive romance arc with Neeshka, who develops quite a lot due to the player character's trust and love.

Web Comics
"Sabine: Sure, women like me swoon for a hero, but that's only because deep down, we think we can change them. But me, I'm done with that now. I want a nice, safe, reliable mass-murderer that I can depend on."
 * In Order of the Stick, Villainous shapeshifter Sabine got over it, describing an inversion of All Girls Want Bad Boys:

Web Original

 * In the first season of The Guild, Zaboo tries to pull this on the protagonist. (When it doesn't work out he instead tries to change himself, but that's a different story.)
 * The Whateley Universe has Loophole getting warned by her advisor that Kodiak isn't going to be susceptible to being changed by her love, and most bad boys aren't. She eventually doesn't try it.
 * Internet punching bag Christian Weston Chandler apparently thinks this is standard operating procedure in a relationship, because he wants to make a girl "a sweetheart from the ground up" (whatever the hell that even means). He doesn't appear to realize how intensely creepy this sounds to people who aren't him (which, admittedly, is about 95% of all his problems).
 * Shows up in a big way on The Nostalgia Chick's top ten list of the hottest animated guys (drawn from the opinions of her fans), which posits that a guy you can change is in and of itself something attractive, related to the All Girls Want Bad Boys archetype. ("What do we like more than a big masculine crusader for justice? A project!" ) It got so bad that her poll turned out The Hunchback of Notre Dame villain Frollo as the tenth hottest animated guy, due almost entirely to the appeal of this trope.
 * She has also railed against the Beauty and the Beast interquels for this: they make it so that Belle is trying to change the Beast, while she notes that in the original, she wouldn't give him the time of day until he took the initiative to start changing himself.

Western Animation
"Leela: Does that dummy have a brother?"
 * In The Simpsons, Marge did this with Homer, and insists it worked. See Page Quote.
 * Inverted in Futurama. Romanticorp tested pickup lines on women using test dummies. One of the dummies used the line "My two favorite things are commitment and changing myself." The woman in the test chamber immediately started making out with the dummy.

"Paul: ...I'm a great guy! I'm unemployed, but that makes her feel useful in the relationship.
 * Parodied on Family Guy in the episode "The Former Life of Brian". Brian tries to impress a recently-widowed mother (only referred to as "Jared's Mom") by putting on a magic show for her son, only to find out that she already has a boyfriend, Paul. They plan to base their whole relationship on this trope:

Jared's Mom: I'm gonna fix him!

Paul: Our relationship will do fine on that basis.

Jared's Mom: If he had his life together, I wouldn't be into it.

Paul: But I don't!

Brian: (exasperated) God, I am so sick of this crap!"

Real Life

 * The version where this shifts to Love Redeems is often averted hard. And in the case of abusive relationships, this mentality has a decent-sized body count.
 * This is also the cause with some spouses who feel they can change their beloved to be their ideal spouse, which usually causes the said beloved to rebel against the changes hard.