Death were one of the first thrash / deathmetal bands. Enough said? Almost.
This clip is from 1987, live in Tampa, performing Scream Bloody Gore, from the album Scream Bloody Gore.
They were quite clearly a massive influence for bands like Slayer, and if you check the images of them from the inside cover of Scream Bloody Gore, you can see how much of an influence their awesome style was as well!