Hammerhead is a gangster that worked for Silvermane and later Kingpin. He has a metal plate made out of adamantium implanted in his head that allows him to attack his enemies by ramming into them with his head.
Not much is known about Hammerhead's early life. At some point Hammerhead had an adamantium plate implanted in his head and discovered that he could use his indestructible skull to ram through objects. Hammerhead then became a gangster and eventually started working as a mob enforcer for Silvermane.
Attack on Silvermane
After Kingpin failed to kill Spider-Man, Silvermane went to Hammerhead and ordered him to organize his men for an attack on Crime Central. However, sometime later Hammerhead approached Silvermane in his headquarters and told him that Kingpin learned of their plans and that he was going to attack them and very soon. A short while later Kingpin's Insidious Six attacked Silvermane's headquarters and attempted to capture Silvermane himself. Hammerhead was able to get Silvermane to an elevator and escape the Insidious Six. As they got on the elevator Hammerhead was actually revealed to be Chameleon. The Chameleon then delievered Silvermane to Kingpin but he was later rescued by Spider-Man.
When Silvermane learned that the Tablet of Time and was brought to New York City he decided he wanted it to make himself young again. Silvermane then sent Hammerhead to the docks to retrieve it. As Hammerhead's helicopter arrived at the docks he and some thugs got out and attempted to steal the Tablet of Time. Spider-Man soon arrived and Hammerhead tried ramming into him with his head. During this Hammerhead was able to get away with the Tablet of Time. However, Spider-Man was able to retrieve the Tablet of Time. Hammerhead then returned to Silvermane and told him of his failure. Because of this Silvermane fired Hammerhead and told him he was bringing in a professional .
Hammerhead later broke into Kingpin's mansion. Kingpin caught Hammerhead and demanded to know why Silvermane sent him. However, Hammerhead revealed to Kingpin that he no longer worked for Silvermane and was looking to be in his employee. Hammerhead then told Kingpin that Silvermane believed the Tablet of Time really had magical powers. Hammerhead offered to get the Tablet of Time for Kingpin. However, Kingpin replied that he did not trust Hammerhead yet but he would consider him for other work.
However, Hammerhead did come up with a plan to get the Tablet of Time for Kingpin. Hammerhead along with two thugs went to the Coffee Bean and abducted Silvermane's daughter, Alisa Silvermane. At that moment Spider-Man was passing by and saw what was going on. Spider-Man attempted to stop Hammerhead but Hammerhead rammed Spider-Man into a hole in the ground and started filling it with cement. Spider-Man managed to escape but failed to stop Hammerhead from taking Alisa. Hammerhead then brought Alisa to Kingpin and told him that she was Silvermane's daughter and suggested that they use Alisa to get the Tablet of Time from Silvermane.
After Spider-Man stopped Silvermane his henchman, Tombstone, used the Tablet of Time to destroy his base. However, the Tablet of Time was saved by Hammerhead who brought it to the Kingpin. Kingpin felt that the Tablet of Time brought him nothing but trouble and ordered Hammerhead to destroy it. However, Hammerhead ended up selling the Tablet of Time to Adrian Toomes.
Hammerhead's skull is surgically reinforced with adamantium, making his head flat on top; with this, he can charge and break through objects such as brick walls without causing any pain or damage to himself. This metal can absorb physical impacts that would otherwise fracture human bone.
In the comics
In the comics Hammerhead's real name is Joseph (his last name was never revealed).
As a young adult Joseph joined the mob as a hitman. When Joseph got into a bar fight his skull was shattered. Before passing out Joseph saw a poster for a movie called The Al Capone Mob.
Joseph was found by a surgeon named Jonas Horrow who had lost his medical license for conducting illegal experiments. Horrow then operated on Joseph replacing much of his shattered skull with a special steel alloy. As Joseph awoke he learned that his steel plated head could be used to ram through walls and other obstacles. Joseph also had amnesia and could no longer remember his name so he took the alias, Hammerhead.
The only thing Hammerhead could remember before the operation was the poster for the movie, The Al Capone Mob. This poster had such an impact with Hammerhead that he began to dress like a 1920's mobster.
Hammerhead eventually led his own crime family within the Maggia and would clash with Spider-Man on several occasions.