Self-Proclaimed Knight

"So, we lie. How did the nobles become noble in the first place? They took it! At a tip of the sword! I'll do it with a lance... A man can change his stars. I won't spend the rest of my life as nothing."

—William, A Knight's Tale

A character wishes to become a knight but cannot, either because of gender, social class, or some other limitation. Thus they either lie about being a knight, or set out to become one in secret, often using a helmet to conceal their true identity. The character's motivation for becoming a knight can vary: sometimes they seek to prove themselves, sometimes they wish to escape another fate, or perhaps they aspires to the ideal and romance of becoming a Knight in Shining Armor or Knight Errant. Often will be known by a descriptive title like "Black Knight" or similar, or may be using a suitably noble sounding alias.

The knight's identity may either be revealed, normally alongside An Aesop about prejudice, or remain a mystery and become some sort of legend that inspires the people. May also involve the character actually being knighted for real at the end for their heroism.

Examples of Self-Proclaimed Knight include:

Film

A Kid in King Arthur's Court reveals its master jouster Black Knight to be the princess!
Two of these end up coming into A Knight's Tale. One is the classic struggling underdog, William Thatcher, the peasant who's masquerading as the knight Ulrich Von Lichtenstein, and the other is the royal in disguise, Sir Thomas Colville or Edward, the Black Prince, who just wants a chance to actually compete and earn something himself instead of being given everything because of his station.
John, a blacksmith and swordsmith, is tutored at Camelot. As a commoner, he can't hope to win the hand of Lady Linet, daughter of the Earl of Yeoniland, so he creates a secret alternate identity as the Black Knight in the 1954 film, The Black Knight.

Literature

Alanna in the first half of Song of the Lioness pretends to be a boy named Alan so that she can train for knighthood. After she earns her shield the lie becomes knows and she leaves in search of adventure.
In A Song of Ice and Fire
- Brienne of Tarth isn't allowed to be a knight because she's a woman, but she fights and acts like knights are supposed to act better than most of the real ones. This has gained her, on the whole, very little respect.
- It's implied that the precursor hero Dunk of the "Dunk and Egg" short stories was never actually knighted by his master. He claims that his master knighted him before he died, but he is repeatedly afflicted by unexplained guilt when the issue gets raised. Ironically, he might be an ancestor to Brienne, given that his arms appear in her father's keep.
- Mystery Knights are tournament competitors who refuse to give their real names, making it ambiguous as to whether they're true knights are not. There are a few examples of people who aren't knights entering the lists as mystery knights, including Barristan Selmy when he was still a squire. There's some evidence that "The Knight of the Laughing Tree" at the Tourney at Harrenhal was actually a disguised Lyanna Stark.
- Ser Osmund Kettleblack, claims he was knighted by "Ser Robert... Stone," which is about as generic and untraceable a name as John Smith.
Don Quixote de la Mancha who reads novels about Chivalry and sets out to revive chivalry as a self-proclaimed knight. This example is Played for Laughs (before the onset of Cerebus Syndrome) as in the time Don Quixote takes place, wandering knights no longer exist.

Live Action TV

Samurai Sentai Shinkenger and Power Rangers Samurai feature an eastern version with samurai. Where the Rangers came from long lineages of samurai, the Sixth Ranger is an old friend of the Red Ranger's; teaching himself to fight and building his own gear to fill a promise to help his buddy. The Rangers are reluctant to involve him in the fighting at first, but they soon accept his help.
Lancelot in Merlin. He isn't a noble, so he can't become a knight, but lies about it to enter the tournament. Uther finds out and only spares his life because he believes Lancelot killed the griffin. Later, Arthur knights him for real. Gwaine zig zags the trope: He is a noble but does not reveal that, so he can't be a knight and eventually gets exiled after trying to stop a couple of guys impersonating knights with magic (further examples of the trope). Later, he gets knighted like Lancelot did.
- Arthur also hires a commoner to act as a knight and enter the jousting tournament. While the commoner, William, would show his face in between jousts it would be Arthur, with his face covered, who actually did the jousting. Arthur does this to show he can win a jousting tournament without any favoritism due to his station.