Marth

Marth is the main protagonist of 4 games in the Fire Emblem role-playing game series. He appears in the first and third games. He has made a total of 5 appearances in the Smash series.

Super Smash Bros.
Marth does not appear in the original Smash game, and there are no mentions of Fire Emblem in the game anywhere. However, Sakurai revealed in an interview that he had a wish to include Marth in the game as a playable character, but he was not able to add Marth due to time constraints. When Sakurai was asked why he considered Marth, he said that he wanted a character who was similar to Link in the style of a swordsman.

Super Smash Bros. Melee
Marth makes his international debut in Super Smash Bros. Melee. In the game, Marth can be unlocked by playing 400 VS matches or using all 14 starter characters in VS. Mode, Classic Mode, or Adventure Mode. Once either criteria is hit, Marth will challenge the player and if defeated, he will be playable.

According to Masahiro Sakurai, Marth was originally planned to be removed from the worldwide copies of Melee along with Roy, and they would only be playable in Japan. However, the development team decided to let Marth and Roy stay in the game.

Super Smash Bros. Brawl
Marth appears in Super Smash Bros. Brawl as a veteran fighter, while Roy would be cut for unknown reasons. Marth can be unlocked by rescuing him in The Subspace Emissary, completing Classic Mode, or playing 10 VS matches. Marth is also joined by Ike in the game.

Super Smash Bros. for Nintendo 3DS / Wii U
In Super Smash Bros. for Nintendo 3DS / Wii U, Marth returns as a playable character along with Ike and Roy, with the latter being a DLC fighter. Marth is a starter character in this game and some aspects of his moveset have been buffed and nerfed. Robin and Lucina also debut as newcomer fighters in the game and they accompany Marth as well from the Fire Emblem series.

Super Smash Bros. Ultimate
In Super Smash Bros. Ultimate, Marth is retained along with the rest of the roster. He was officially confirmed on June 12, 2018. Marth is also an unlockable character who can be obtained by playing World of Light, beating Classic Mode twice as Yoshi or Lucario, or playing 1 hour of VS matches and having 6 characters unlocked. Marth now speaks in English.

Trivia

 * Marth is the only playable Fire Emblem character to debut in the 20th century.
 * Marth is the fastest walker in the series.