Gilgamesh was an ancient Sumerian king who ruled Uruk, modern day Iraq around 2650 BC. He is the main character of the Epic of Gilgamesh, which is considered one of the earliest works of literature, the most complete edition dating back to the 7th century BC, though earlier editions date back to about 2000 BC. The epic centers around the king and demigod Gilgamesh and the wild man Enkidu who was sent to kill him. After a fight between the two, in which neither Gilgamesh nor Enkidu prove themselves stronger, they become loyal friends and embark on several epic adventures. During their quest Enkidu is wounded by a Mythical Bull, and dies after twelve days of suffering. Gilgamesh resolves to find a way to revive his friend, and after a long and treacherous quest finds a plant that can bestow eternal life. However, it is eaten by a snake when Gilgamesh stops to bathe and puts the plant down. Though despairing the loss of the chance to save Enkidu, Gilgamesh learns a valuable lesson, that true immortality can be gained by leaving a legacy for others to learn from and aspire to.
Gilgamesh from Final Fantasy is often portrayed with additional arms, which parallels with the multiple arms the historical Gilgamesh is often portrayed with. Enkidu, in turn, appears alongside Gilgamesh in bestial form, which likely refers to the wild and formerly untamed nature of Enkidu.
Gilgamesh is also inspired by Saitō Musashibō Benkei, a famous Japanese warrior monk said to have posted himself at Gōjō Bridge in Kyoto and dueled every passing swordsman, defeating 999 opponents and claiming their weapons. His 1000th opponent was Minamoto no Yoshitsune who defeated Benkei and made him a retainer, and the two went to war with the Taira clan. Years later the two were encirled in the castle of Koromogawa no tate, and Yoshitsune went inside to commit ritual suicide while Beneki defended the bridge to the castle. Benkei killed all warriors who attempted to pass, and eventually died standing up, riddled with arrows and wounds.
From the story of Benkei, Gilgamesh takes his preference for the naginata (Benkei's traditional weapon as a monk), his penchant for fighting on bridges, his collecting of weapons from enemies he defeats, and his friendship with the player's characters who defeat him. Benkei's devotion to Yoshitsune is the basis for Gilgamesh's association with Genji equipment—the Minamoto Clan is also called the Genji Clan, using the alternate pronunciation for the Chinese characters for mina and moto, gen and uji, respectively. Gilgamesh's face paint is based on traditional kabuki actors, for which Benkei is a popular character to portray.