The Truth, is a main character encountered in Grand Theft Auto: San Andreas in the coutryside. For more information about The Truth as a character, check out The Truth on the GTA Wiki. This page describes about him as a myth.
Background
The Truth is a hippie who has deep distrust of government and is a conspiracy theorist. He lives in Leafy Hollow, Flint County where he operates a marijuana farm which he and CJ destroy (burn) in the mission Are You Going to San Fierro? after the police find out about the weed operation. He says that he has tried for 30 years to break in to Area 69 and get a top secret project known as "Black Project". He uses CJ to thus break in to Area 69 and steal a jetpack and a containment unit that contains an unknown substance called "Green Goo". He also calls in on the WTCR radio show and claims to have held Aliens in his hands, which might be related to the Green Goo.
Omega from GTA V bears a strong resemblance to The Truth. Both are conspiracy theorists and hippies; and both believe in extraterrestrials. Also, they both say that they have seen Aliens, along with Unidentified Flying Objects.