The Chooser of the One

Lana: So how is it that you're important enough to know about this prophecy, huh?!
Turrick: I wrote it.

—Anti-HEROES

Like the name says, the Chooser of the One is the character who finds and chooses The Chosen One. The Chooser can go about this a few different ways. They may possess a book or prophecy that describes The Chosen One, or a means of picking them out of a crowd, or they may be a prophet or seer of some kind who can sense the One. Once found or selected, the chooser may take on the role of Mentor and start training them, tell them of their destiny, or simply deliver the Call to Adventure and hope they accept it.

Sometimes, the Chooser isn't charged with finding the One, so much as finding a One. The Chooser essentially looks for someone with the skills to fill a job description (defeating the Big Bad, saving the world, etc) and goes with their gut rather than on divine mandate. A knight searching for someone to Take Up My Sword may simply look for anyone who has the right amount (get it?) of pluck and decency. In these cases the person picked may be more of an Unchosen One who chooses to create their destiny rather than sit by passively.

If the Chooser is a god or Enigmatic Empowering Entity they may do the designating themselves rather than via prophecy, Super Empowering the chosen from a complete random Muggle into the One. Other possible Choosers are Sentient Phlebotinum, an Empathic Weapon, The Force or God(s).

Because of this potential for plot induced randomness, there can be an exploration on the true nature of heroism as something innate or vocational, and destiny as immutable or malleable. It's possible that the Chooser could invoke a sort of Koan and claim that the mere act of choosing someone is meaningless, rather the faith and trust of the chosen paves their path... or that there is no randomness, only destiny.

Compare and contrast The Presents Were Never From Santa, which is when a character thinks they have supernatural aid or a helper, but don't.

Examples of The Chooser of the One include:

Anime and Manga

Kirin in The Twelve Kingdoms choose each nation's king. The real deciders are gods, but the kirin never make a mistake, even if they think they did.
Naruto: Jiraiya was prophesied to train The Chosen One who would either bring peace or destruction. Considering all of his other candidates/trainees are now dead and neither has happened yet, the titular character is now the one by default.
- Though he did consider Naruto The Chosen One anyway even when one of his students, Nagato, who wielded a legendary godlike power, was still alive.
Chi is responsible for choosing The One Just For Me which beyond simple happiness for her and that one, activates a poetentially dangerous program.
Played with in The Slayers TRY. Lina is approached by a dragon priestess to save the world from destruction. Lina brags about how OF COURSE she'd come to her first. At this point, the priestess announces that Lina was actually their second choice.

Comic Books

Green Lanterns are chosen by their ring for their ability to overcome great fear. Usually the living planet Mogo adds in a moral component to the criteria so villains who can overcome great fear aren't chosen. Later Hal Jordan destroyed the corps and all but one of the Guardians of the Universe, Ganthet. He forged one last ring and choose the next, last lantern on his own and almost seemingly at random with a glib "You'll have to do." Years later, after Kyle relit the Central Power Battery and resurrected the Guardians, Ganthet had this to say:

Ganthet: You, my boy, my last lantern... you have always been my greatest hope.
Kyle Rayner: No kidding? When you gave me that ring you said "you shall have to do."
Ganthet: I don't remember anything like that-- I have always had the greatest faith in you.
Kyle Rayner: Sounding like a parent already.

Film

The wise turtle Master Oogway from Kung Fu Panda is the one who chooses Po the panda as the next "Dragon Warrior".
The Matrix: Morpheus discovered and mentored Neo. The Oracle can't choose the One, but is able to tell whether Neo is or isn't the One. The Architect would probably be the chooser, because he programmed Neo to be the One.
In Star Wars: The Phantom Menace, Qui-Gon chose Anakin. (discover correct choice)
In the original Buffy the Vampire Slayer movie, Merrick is essentially this, being the one who finds Buffy and tells her she is the chosen one.
The Sidekick in Puma Man is also the one charged with finding the chosen one to become the eponymous hero.
In Captain America: The First Avenger, Dr. Erskine overhears a conversation between Steve Rogers and Bucky, and realizes that Steve is the perfect candidate for the Super Serum.

Literature

The Chronicles of Narnia: Aslan chose the children.
In The Hobbit, Gandalf chooses Bilbo to be the group's thief, even though Bilbo has never been on an adventure before and doesn't want to go on one now. It turns out to be a good choice.
Cyradis the Blind Seer in the Malloreon series by David Eddings is responsible for choosing between The Hero and the Big Bad at the final showdown.
In Harry Potter, Voldemort was unknowingly the Chooser, since whoever he decided to mark "as his equal" would be the one with the power to defeat him. Technically, it could have been either Harry or Neville, or no-one, but Voldemort made it final.
In Legend of the Seeker, Zedd names Richard as the Seeker.
- There's some bias here as well, given that he is Richard's maternal grandfather.

Live-Action TV

In Once Upon a Time, Prince Charming chose Emma by placing her in Gepetto's machine, but she had to be re-chosen by Henry in order to receive the Call to Adventure.
Rupert Giles, and also the demon Whistler in Buffy the Vampire Slayer
Doyle, on Angel, sent by the powers, as Whistler was on Buffy, to tell Angel he was a chosen one.
This was basically Azazel's role in Supernatural. First, he chose a variety of kids who were possible candidates. Out of this group, one of them would be chosen ultimately. The idea was that the chosen one would not only free Lilith from hell, but also be instrumental in releasing Lucifer as well as become Lucifer's vessel.

Oral Tradition, Folklore, Myths and Legends

In The Bible, the prophet Samuel chose the first two kings of Israel, Saul and David, led by God.
- This happens often in Genesis. G-d chooses Abraham. He also chooses Jacob while Jacob and Esau are still in the womb and tells Rebecca about it, leading to her knowing which son to favor. Jacob favors Joseph out of his twelve sons, and Joseph ends up receiving prophetic dreams and the ability to interpret the dreams of others. In Exodus, G-d chooses Moses to lead the Israelites, Moses's elder brother Aaron as spokesman and later High Priest, and Moses's older sister Miriam as another prophet and third leader of the people.

Tabletop Games

Sorcerers of Tzeentch in Warhammer Fantasy Battle can use a spell called Call to Glory. It turns a normal guy into an Exalted Hero.

Video Games

In Mortal Kombat 3, Raiden designated several characters as his chosen during Shao Kahn's invasion of Earthrealm, preventing their souls from being taken by Shao Kahn's Soulnado and allowing them to mount a counterattack against the invaders. This group consisted of Liu Kang, Kung Lao, Johnny Cage (Back from the Dead after being killed by Kahn's extermination squads due to the Soulnado preventing passage into the afterlife), Sonya Blade, Jackson "Jax" Briggs, Younger Sub-Zero, Smoke (much to his surprise), Nightwolf, Kurtis Stryker, and Kabal. Presumably, the same applies to the Forces of Light in Mortal Kombat 9, which consisted of most of the same characters (key differences being that Kung Lao had been killed off by Kahn in the climax of the MK2 arc, Sub-Zero had been captured by the Lin Kuei and turned into a cyborg instead of Smoke, and Kitana and Jade had joined the Earthrealm heroes prior to the events of 3).
EarthBound has Buzz Buzz who came from 10 years in the future, and he chooses Ness as the Chosen One.
Gwonam in Link: Faces Of Evil

Gwonam: "It is written: "Only Link can defeat Ganon".

Duncan in Dragon Age who in each origin arrives seeking new recruits for the Grey Wardens, ultimately choosing The Warden.

Web Comics

In Drowtales, Ariel is chosen by Quain. As of the end of chapter 32, it appears that Chrys has been chosen by Sillice.
In Rice Boy, T-O-E is the last of a group of three searchers, given a divine mandate to find and designate the Fulfiller of an ancient prophecy. The twist is that T-O-E's word is no indication that a chosen individual will actually fulfill the prophecy. One of the other searchers, Calabash, quit the job precisely because he was tired of choosing Fulfillers who go Knight Templar or mess up just as bad in some other fashion.
- Possible subversion in that Rice Boy himself points out all the ways T-O-E himself has fulfilled the prophecy, and it is T-O-E who makes the Heroic Sacrifice that saves the world and ends the gigantic battle.

Web Original

In The Gamers Alliance, the elven cleric Schuldich Cedheros is the sole survivor of the massacre of his order and is sent by the Gods of Order to find wielders for two special enchanted weapons, Dusk and Dawn, which the chosen ones will be destined to use to fight the forces of Chaos. Schuldich manages to deliver Dusk to its intended bearer but narrowly fails with Dawn (he did find two candidates for Dawn's intended bearer but before he could figure out which of the two women were meant to have the sword, an evil goddess appeared, killed him and stole the sword right in front of the women's noses).
- Leon also ends up in this role when he is tasked with finding the bearer of the Silver Branch whose destiny is to stop the Landpoison of Yamato and heal the wound on the earth caused by the dark god Mardük's tainted magic.
The Questport Chronicles: The Lord of the Supreme Council sends the eight strangers that show up at the Temple out on a quest, on the basis that if a real hero hasn't shown up by now, it's unlikely that one ever will. She takes some flak from the rest of the Supreme Council for it, but it works out.

Western Animation

In Miraculous Ladybug, the role of Guardian of the Miraculouses (the one in charge of deciding who can be trusted with them) in initially held by Master Wang Fu, who gave Marinette and Adrien their Miraculous-es after both passed a Secret Test of Character. Later, he tended to trust Marinette to "lend" them out if the need arose, as she knew a lot more about her peers and knew who could be trusted not to abuse the powers. (Not that her judgement was perfect, of course.) As of the episode "Miracle Queen", Marinette is the official Guardian of the Miraculouses, after Fu officially retires and names her his successor.