Slayer, Metallica, Anthrax and Megadeth are often referred to as the “Big 4 of Thrash Metal”. These bands were the most visible and, many feel, the most influential of the thrash bands to emerge in the early-to-mid 1980's. The thrash sound was somewhat new, and these bands were seen as the leaders of a movement. Many of their albums have stood the test of time as metal masterpieces.
There were other bands that made a big impact as well, most notably Exodus and Testament. Later, bands such as Sepultura and Pantera picked up the torch.
All of these bands made great music. They influenced millions of musicians and fans. However, it’s tough to argue that any did so more than the Big 4 of Slayer, Metallica, Anthrax and Megadeth.