All my life, every time I've ever believed in anything, or had faith that the future would get better for me, I've had that false hope knocked out of me... and found myself back on my knees in despair. I have nothing left to believe in or to live for... not even myself. Nick, give me your gun. Goodbye, Nick.
Jacob "Jake" Fury, younger brother of Nick Fury, has been known both as the criminal Scorpio and undercover as the terrorist leader Kraken. He grew up in Depression-era New York City with his brother and younger sister Dawn. Fury's mother died while he was very young and his father Jack Fury, an American pilot who joined the British war effort during World War I, remarried. The children were raised by their stepmother after Jack Fury's own early death. Living in the tough streets of Hell's Kitchen, Fury and his brother were no strangers to trouble.
Jake was 17 during the attack on Pearl Harbor, the year his brother officially enlisted. Jake would be opposed to the war until three years later when his family got caught up in the revenge plot of the Nazi spy, Colonel Klaue, who was targeting Nick while he was visiting home on a week pass. After seeing the Nazi threat firsthand, Jake decided to enlist the next day.  He would later regret the decision following unpleasant experiences in the Army. 
Each mission involved acquiring advanced technology from around the world. Jake executed a mission with his brother and Thomas Davidson to Chapel at Chateau D'Amboise in France, where they found the technology that would later be reverse-engineered into Life-Model Decoys (LMDs). Jake unwisely got too close and activated it. The technology latched onto him and Davidson, creating Life-Model Decoys of them both. Nick decided to keep this a secret.
Now believed dead, Jake helped his brother in the secret war against Hydra and Leviathan. He remained underground for years despite his LMD committing acts of terrorism as Scorpio.
At one point, Jacob Fury went to the Kraken's home in London. Jacob knew Daniel Whitehall, but did not know him as the Kraken. In the London house, Jacob found the his journals and learned his entire evil history.
Jacob tracked down the Whitehall, who lay dying in a hospital. There he took the Kraken's helmet, over Whitehall's objections, and wore it himself. The helmet grew down Jacob's body, covering him in the Kraken's green armor. The new Kraken killed Daniel Whitehall by shutting off the machines keeping him alive. Jacob then infiltrated Hydra's leadership.
Due to the old Krakens's secretive past he was able to convince Baron Strucker that he was the original. He provoked an all out war between Hydra and Leviathan and a civil war within Hydra. After arranging Baron Strucker's death, his role in his brother's plans was almost complete. He completed his final task, delivering a letter to Daisy Johnson (Quake), and then disappeared.
Infinity Formula: Jake Fury's aging has been slowed greatly by the Infinity Formula, a serum created by Dr. Berthold Sternberg. Close to 90 years old, Jake maintains a middle aged athletic physique, perhaps due to a chronic low-level exposure to the Infinity Formula in Nick Fury's bloodstream.
Jake Fury is an experienced warrior, highly skilled in espionage (especially in disguise) and hand-to-hand combat.
Jake Fury possesses the normal human strength of a man of in his middle-age years, and with his own height and build who engages in extensive regular exercise.
Kraken Armor: Upon donning the Kraken's helmet, The helmet altered his appearance and voice, as well as covering him in the Kraken Armor, which apparently enhanced his strength and durability, enabled him to transport himself and several across inter-continental distances (perhaps via accessing other technology) presumably granted him energy projection and other abilities as well. The helmet may also affect the mind of the wearer, as the Kraken described feeling like he was "slipping into a new persona - a new face, a new voice... and the vision to see the world in a new light." The helmet also protected the Kraken from Gorgon's stone gaze, though that may have just been by dint of preventing eye contact.
Jacob Fury's early appearances are reprinted in various comics.