Gunstar Heroes is a 1993 run and gun video game developed by Treasure and published by Sega for the Sega Genesis. It was Treasure's first developed video game. The premise is centered around a pair of characters, the Gunstars, in their efforts to stop an evil empire from recovering four powerful gems. The characters can fire guns and perform a series of acrobatic maneuvers to fight enemies across each stage. There are four weapons which can be combined with one another to create different shot types.

Development on Gunstar Heroes began among a team of staff working at Konami in 1991. Following an unwillingness of Konami to embrace their original game ideas, the team quit in 1992 and formed Treasure to see their project through. The team wanted to develop their game for the Genesis because of the system's powerful Motorola 68000 microprocessor. Sega initially rejected their proposal, but later granted approval after they worked for Sega for several months on McDonald's Treasure Land Adventure (1993). Treasure worked on both games in parallel, and released Gunstar Heroes as their first game in 1993.

Gunstar Heroes was a critical success, being praised for its frantic action and advanced graphics. It helped establish Treasure's place in the industry, and introduced numerous design conventions which would become characteristic of their later work such as large bosses and a unique sense of humor. It was re-released several times, including dedicated ports to the Game Gear and Nintendo 3DS, and received a sequel on the Game Boy Advance. In retrospect, it is considered one of the best action games of the 16-bit era, and one of the best video games of all time by several publications.

Gunstar Heroes is a run and gun game which is played from a side-scrolling perspective similar to Contra. The game can be played in single-player, or cooperatively with a partner. The players take on the role of Gunstar Red and Gunstar Blue as they battle with an evil empire for control over a set of powerful gems. The game features seven stages, of which the first four can be played in any order. The stage formats vary. While some feature a left-to-right format, others include the player riding in a mine cart along walls, fighting enemies on a helicopter, or playing a board game. Completing a level grants the player an extension to their maximum health, known as vitality in the game.

When starting the game, the player can choose either a free or fixed firing stance; the free stance allows the player to move in the direction they are firing, while the fixed stance immobilizes the character when shooting. The player also has a choice of starting weapon. There are four shot types in the game: a homing shot, lightning blaster, flamethrower, and machine gun. Every weapon has its strengths and weaknesses, and can be swapped with others from item drops. The weapons can be combined with each other to produce unique shot types. For example, the homing shot can be combined with the machine gun to add a homing effect to the latter, or two lightning shots can be combined to create a more powerful lightning gun. In addition to firing their weapon, the player characters can perform a series of acrobatic maneuvers including jumping, sliding, and grabbing and throwing enemies.

In 1991, several Konami employees led by programmer Masato Maegawa began holding planning sessions at coffee shops for an original game. They were establishing early concepts for an action shooting game, a genre they were familiar with. They pitched their idea to Konami, but were told it would not sell and it was rejected. Maegawa and his team were growing frustrated with the industry's reliance on sequels to established franchises and console conversions of arcade games to generate revenue. They felt Konami had fallen into this pattern as a large company, growing reliant on sequels in their Castlevania and Teenage Mutant Ninja Turtles series. Maegawa and his team felt consumers wanted original games, and so in 1992, they left Konami and established Treasure to continue development on their unique game.

Treasure wanted to develop their game for the Sega Genesis. Maegawa liked the platform because of its Motorola 68000 microprocessor, which he felt was easier to program for than the Super NES, and more powerful. The team decided to approach Sega for a publishing contract. When they presented their design documents to Sega, they were not granted approval because they lacked a proven track record. Instead, Sega contracted Treasure to develop McDonald's Treasure Land Adventure (1993). Several months into development, they were granted approval to work on their game. They were initially using the working title Lunatic Gunstar, thinking "Lunatic" was a good description of the stimulating action. Sega of America felt the word held a negative connotation, so rejected it. The team also considered Blade Gunner, in homage to Blade Runner, but this was also rejected due to copyright restrictions. Sega of America eventually suggested the word "Heroes", so Gunstar Heroes became the final title.

Treasure consisted of around 18 people, most being programmers from Konami. The staff was split in half to work on both Gunstar Heroes and McDonald's Treasure Land Adventure in parallel. The core team behind Gunstar Heroes consisted of six people: two programmers, two graphic designers, and two sound programmers. The staff (known by their nicknames) was composed of main programmer Yaiman, enemy and boss programmer Nami, graphic designers Han and Iuchi, composer Non, and sound effects programmer Murata. The role of game designer did not exist within Treasure. All game design and planning was undertaken by everyone involved. The team felt they had more freedom working under Sega than Konami. Maegawa got approval to add a Treasure logo when the game booted, which he felt was a rare opportunity for developers to receive during that era.