The wonderful thing about Jackhammer, is that Jackhammer's a wonderful thing. His head's made out of a piston, his lower body's a spring. He's bouncy, trouncy, flouncy, pouncy, and full of fun fun fun. But the most wonderful thing about Jackhammer - as far as the Autobots are concerned - is that he's the only one.
Marvel comic continuity
Jackhammer was part of the group of mutants who chased the young Autobots Tailgate, Flattop and Subsea through the Underworld when the trio foolishly decided to take the ancient Autobot "trial by fire".
Using his head to bust into the Autobots' hiding place, he introduced himself and Warhead, watching as the latter killed Subsea. Tailgate slugged him for his trouble, and he died shortly afterwards when the Autobot shot Smeltdown's furnace, causing a massive explosion. His carcass was subsequently eaten by Cybertron's dreaded subterranean demons. Their hunger only whetted by Jackhammer, the demons then began to feed on Cybertron's surface-dwellers.