Marth

"I am a prince before I am a son or brother."

- Marth's quote in Shadow Dragon.

Marth is a hero from the Fire Emblem series of video games. He is the central protagonist and Lord-class character of the original game, Fire Emblem: Ankoku Ryū to Hikari no Tsurugi (Shadow Dragon and the Blade of Light) and Monshō no Nazo (Mystery of the Emblem), as well as their respective remakes. Although Marth's two titles were released only in Japan at the time, he has acquired more widespread international attention through his appearance in the Nintendo brawler, Super Smash Bros. Melee. The appearance of Marth and Roy sparked a greater level of western interest in the Fire Emblem franchise, and it was in part because of this that Nintendo began releasing the games internationally beginning with Fire Emblem: The Blazing Blade, the seventh title in the series.

Fire Emblem: Shadow Dragon
Marth appears in Fire Emblem: Shadow Dragon and the Blade of Light as well as its remake (New) Shadow Dragon, taking the role as the main protagonist. This game showed Marth fleeing his country of Altea after being invaded by a previously allied nation, Gra.

Marth began building up an army by convincing some members of enemy forces to join him, as well as receiving military assistance from some allied kingdoms. He led his army, called the Akaneian League, to conquer the countries of Gra, Grust, Macedon, Khaden, and Dolhr. In the process, he killed the shadow dragon, Medeus, and saved humankind.

This game explains how Marth is a descendant of the great hero, Anri, who was blessed by the god Naga to save humankind in a very similar way to Marth. Since the blessed blood of Anri runs through his veins Marth is able to wield the dragon-slaying blade of light, the Falchion. This blade matches the power of the strongest normal sword (the silver sword) with the additional effect of doing extra damage to dragon units and being indestructible.

Fire Emblem Awakening
Marth first appears in Chapter 1 as a masked identity saving Lissa from an attacking Risen. He is once again encountered when Chrom arrives at Arena Ferox to prove his strength. In reality, "Marth" is a woman who traveled back in time to save her future. The true Marth appears in three different Einherjar forms: two StreetPass units, Pr. Marth (Prince Marth) and King Marth respectively, and a third DLC form in Champions of Yore 1.

In Champions of Yore 1, he helps Chrom fight the female heroes of previous Fire Emblem games, ending with Celica. Marth can join after completion of the Xenologue chapter. He appears yet again in Champions of Yore 2 and 3, only this time hostile and in his Shadow Dragon form per the portraits which Old Hubba explains is another reflection of the Hero-King with different abilities. Marth asks the Shepherds if they came to kidnap Aversa, to which he suggests they leave before harm comes to them. In defence, Old Hubba says they are no kidnappers who would even think of torturing her. Chrom reminds him about mentioning the Einherjar cannot be reasoned with, and Marth expresses being fed up with lies, telling the Shepherds to draw their weapons and die with honor.

Marth continues to appear throughout the Einherjar tale until Rogues & Redeemers, first as an ally before becoming a hostility in the last two parts.

Fire Emblem Fates
Marth makes another small appearance, this time as an amiibo unit. His Lodestar class has been given a unique look compared to reusing Lucina's Masked "Marth" model without her mask.

Super Smash Bros
Marth is a playable character in those games.

Trivia

 * Marth was originally considered for Super Smash Bros. 64 according to the creator, Masahiro Sakurai.
 * Since Marth's games had never been released outside Japan, his international debut is considered to be Super Smash Bros. Melee. His and Roy's franchise would not see overseas release until Blazing Blade.
 * In Awakening, Marth's appearance uses Lucina's resources while masquerading as him, only the mask is removed.