Be My Valentine

Because of the holiday, there is an inherent sort of romanticism associated with the name "Valentine".

Writers will utilize this association to hint at the character's heroic roots. The Knight in Shining Armor named Valentine will do anything to win fair lady's hand, while an Anti-Hero or The Stoic may have the name in order to hint at his Hidden Heart of Gold. A girl with a Sugar and Ice Personality named Valentine will often become a Defrosting Ice Queen.

A Villain with the name "Valentine" is often a deliberate subversion on the audience's subconscious expectations, though they do often keep some level of tragic romanticism. They will often be a Well-Intentioned Extremist, or perhaps a Noble Demon or Worthy Opponent. Female villains may be The Vamp.

May or may not apply to slight variations (Valentino, Valentin, etc.) depending on their characterizaton.

A naming convention. Compare Cherry Blossom Girl and Alice Allusion.

Anime and Manga

 * Faye Valentine from Cowboy Bebop.
 * Mai Valentine from Yu-Gi-Oh. Her last name is Kujaku (peafowl) in the original, though.
 * U.S. President (and Big Bad) Funny Valentine in JoJo's Bizarre Adventure: Steel Ball Run.

Film

 * The grandfather in Spy Kids (played by Ricardo Montalban) is named Valentin Avellan.
 * Kevin Bacon played Valentine "Val" Mckee in Tremors.
 * Valentine from Mirror Mask isn't romanticized, but he does fit the "anti-hero with a heart of gold" type.
 * Gangster Eddie Valentine from The Rocketeer. Technically a bad guy, but throws his hat in with the heroes once he learns his employer is a two-bit Nazi.
 * Valentin Zukovsky is an ally of James Bond who isn't quite evil but not entirely good either.
 * Billy Ray Valentine in Trading Places

Literature

 * Valentine Wolfe, who never met a drug he didn't like, from Deathstalker.
 * Robert Heinlein's Stranger in A Strange Land has Valentine Michael Smith.
 * Valentine Wiggin from Ender's Game. Valentine is the sweet, empathetic-to-a-fault middle child. This stands in contrast with her brothers psychopath-but-he-grew-up-okay Peter "The Rock (Upon Whom I Found My Church)," Fisher Of Men, and the youngest practically-inhuman-empathy-and-perfect-warrior 'Ender,' properly Andrew, "brother of Peter", "he-who-insisted-on-being-crucified-on-an-X". You see, their father—the very-Catholic John Paul Wiggin —gave them significant saints' names and secret baptisms, because Ender's Game was written at a time when Card seriously believed that Da Gubbamint might outlaw the practice of religion and succeed under the pretense of population control. This interacts annoyingly with The Great Politics Mess-Up, for reasons that have nothing to do with this trope.
 * The heroine of the very first of PG Wodehouse's "Blandings Castle" novels, Something Fresh (1915), was named Joan Valentine.
 * The real name of reformed safe-cracker Ralph Spencer in O. Henry's "A Retrieved Reformation" is Jimmy Valentine. (The story was filmed twice, in 1915 and in 1928, as Alias Jimmy Valentine.)
 * In G. K. Chesterton's "Father Brown" stories "The Blue Cross" and "The Secret Garden," Aristide Valentin [sic] is the Head of the Parisian police.
 * The main character of Robert Silverberg's Lord Valentine's Castle, and some but not all of the following books in the Majipoor series.
 * Mortal Engines has Thaddeus and his daughter Katherine.
 * Valentine de Villefort, the Proper Lady-like daughter of the Count's enemies in The Count of Monte Cristo
 * And her counterpart in the anime series Gankutsuou, based on The Count of Monte Cristo.
 * Valentinian in Belisarius Series. He does not have a particularly romantic outlook on life.
 * Valentine Morgenstern in Cassandra Clare's Mortal Instruments series is not a nice person.

Live-Action TV

 * Becca Valentine from Andromeda.
 * Emily Valentine from Beverly Hills, 90210
 * Cat Valentine from Victorious.
 * Emma Valentine from The Wild Wild West episode "The Night of the Vicious Valentine". She's a . And she wears heart-themed clothing.

Music

 * "The Two Sides of Monsieur Valentine", by Spoon. The song is quite cryptic (and good!), but Monsieur Valentine is mentioned to have a "black heart machine".

Professional Wrestling

 * Greg "The Hammer" Valentine, son of Johnny Valentine.

Theatre

 * Valentine, one of the Two Gentlemen of Verona from the play of the same name by Shakespeare

Video Games

 * Jill Valentine in the first, third, and fifth Resident Evil games.
 * Vincent Valentine from Final Fantasy VII
 * Isabella (Ivy) Valentine, from the Soul Series series.
 * The family of vampires from Shadow Hearts.
 * Mr. Valentine, the Big Bad arch-criminal from Guilty Party.
 * Queen Valentina from Super Mario RPG.

Web Comics

 * Valentine Liosbri of the web comic HERO.

Web Original

 * Renee Valenti from Survival of the Fittest.

Real Life

 * Once famous as the greatest lover in film, Rudolf Valentino.
 * The original Saint Valentine.
 * Truthfully there have been about thirty saints named "Valentine" (and a few Valentinas) but the most likely candidates for the inspiration for St. Valentine's Day was the Third Century Roman martyr detailed here.