Level 1 Music Represents

The background music of the first level in many videogames frequently becomes the theme associated with the series. Sometimes, the "first level" theme becomes so representative of the series that it supplants the planned Main Theme in later games and advertising material. After all, chances are that people will spend more time on the first level learning the ropes rather than admiring the title screen. This trope is more common in linear games (like platformers and shoot-em-ups) as opposed to Sandboxes or RPGS.

A Sub-Trope of Bootstrapped Theme.

Straight Examples:

 * Super Mario Bros: "Ground Theme", also known as the Overworld theme. Pretty much the most well known example and the Trope Codifier.
 * Subverted in Super Mario Bros. 2, as well as in Super Mario All Stars (which gave title themes to all the games that didn't have one). Their respective title themes were all renditions of the underwater music.
 * Sonic the Hedgehog: Green Hill Zone. The original title theme never appears these days unless as a throwback.
 * The Legend of Zelda: Hyrule Overworld.
 * Kirby: Green Greens
 * F-Zero: Mute City.
 * Kid Icarus: Underworld. It has the same intro as the title screen music, but the two themes differ from there.
 * Castlevania: Vampire Killer.
 * Donkey Kong Country: "DK Island Swing", also known as "Jungle Level", "Jungle Groove", or by its stage moniker, "Jungle Japes". Slightly unusual in that the music changes tone halfway through in the original game but only the first half is usually remembered.
 * Metroid: Brinstar.
 * Doom: At Doom's Gate
 * Star Fox: Corneria.
 * R-Type: R9, To the Front!
 * Ghosts N Goblins: Haunted Graveyard, which was used as Arthur's theme for Namco X Capcom and Marvel vs. Capcom 3.
 * Final Fight: Guy's theme in Street Fighter Alpha (as well as in his later fighting game appearances) is a rendition of BGM 1.
 * Raiden: "Gallantry".
 * Gradius: "Challenger 1985", whose melody also appears in the intro to the Stage 2 music for Gradius V.
 * Blaster Master: "Area 1 (Forest)"
 * Journey to Silius: "Space Colony Ruins", which is better remembered than the title theme (although the former uses the same bassline as the latter in its refrain) and is reused for the last stage.

Subversions, aversions, and inversions include:

 * Averted in every game that uses the "Title Screen" music as the main theme in subsequent games.
 * The Bionic Commando theme appears to be a straight example, being the zone 1 music from the NES game but in the original arcade game the music is used on the second level.
 * The Mega Man series is all over the place with this trope:
 * Mega Man 1: Cut Man's theme is a straight example as it is usually the first level selected.
 * Averted and subverted in Mega Man 2 where the title theme is used to represent Mega Man in Marvel vs. Capcom Clash of the Superheroes and the other iconic theme is the first level...of the boss's fortress.
 * The Mega Man Legends subseries averts this by having The Flutter Vs. Gesellschaft theme from later in the game as the Iconic theme.
 * Double Dragon: the title theme is played during the final boss battle, but during the bonus sibling match that occurs when two players complete the game together, the music changes to the Mission 1 theme. This also holds true to the NES version, which has Machine Gun Willy as the penultimate boss and Jimmy Lee as the final boss.