Mammoth is a vehicle manufacturer that appears in GTA 6.
The company made its first appearance in GTA 4, returning in GTA: Chinatown Wars, GTA 5, and GTA Online.
It was confirmed to return once again in Trailer 1, where a 
Mammoth is known for its line of Hummer-style vehicles, though neither the Patriot nor the Squaddie have been spotted in GTA 6 so far.
The company also manufactures a range of aircraft, from seaplanes to military fighter jets. Mammoth is also the developer of the Thruster, GTA 5’s only jetpack, suggesting that it has a contract with the United States government in-universe.
Mammoth appears to be primarily be a reference to the real vehicle manufacturer Hummer, or perhaps its original owner, AM General.
Its name references the prehistoric creature known for its enormous size, which is likely a nod to the overcompensating nature of Hummer SUVs.
