Rumors of Bigfoot being found in Back O' Beyond surfaced within a week of the game's release. Although no definitive proof of Bigfoot's existence was ever produced and Rockstar Games eventually confirmed that Bigfoot did not exist in the game. However, they hinted something was there, which fueled many gamers to continue the search. However, the release of modifications made the search near-impossible, as anything considered "evidence" of his existence was most likely taken out of a modified version of the game. Bigfoot remains arguably the most popular myth of the GTA franchise. Possibly for this reason, Bigfoot was introduced in the next game taking place in San Andreas, GTA V.
The mission's objective is to hunt the O'Neil brothers in the woods of Cassidy Creek using a rifle with thermal scope. At the lower right corner you can see Bigfoot standing still. He will immediately disappear after he has been spotted. If Michael tries to shoot at it nothing happens. This serves as an easter egg.
The mission is dedicated entirely to Bigfoot. Franklin meets a hunter who says that he has been on a sasquatch's tail for eight years (GTA San Andreas had been released 9 years prior to GTA V). After searching the woods, the creature can be seen running. After a long chase, he will reach a dead end and will start cowering in fear. Upon shooting him, he will repeat the phrases "shoot me human" and "I'm the last of my kind" (This is a throw back to the sasquatch mission in Red Dead Redemption). Franklin concludes that the so-called Bigfoot is nothing more than a crazed man in a costume.
On the PS4, Xbox One and PC version, after the player beats the game to 100%, completes the Strangers and Freaks mission The Last One and finds all 27 Peyote Plants, a special Golden Peyote Plant which only spawns at the Raton Canyon in Chiliad Mountain State Wilderness on Tuesdays, from 5:30 to 8:00 AM with the weather set to Snow (consoles, unlocked only by a cheat code) or Foggy (PC version) will be unlocked. This special Peyote Plant grants the player the ability to play as Sasquatch himself. Bigfoot works almost identically to human characters, can drive any vehicles, can use any dropped weapons, and has increased strength.
GTA V: Predator.
GTA V: The Last One.
Being controled by the player using the Golden Peyote.
In Red Dead Redemption: Undead Nightmare, one can get an achievement for killing a sasquatch called Six Years in the Making. This is a reference to Grand Theft Auto: San Andreas, as Red Dead Redemption was made six years after Grand Theft Auto: San Andreas.