Jack

Jack was a corrupt ex-cop, who was Frank Delano's bodyguard and chief enforcer. He acted as the third-in-command of Delano's crew.

Early life
Nothing is known about his early life, although it is known that he was once a career detective in HPD before presumably being fired for corruption. He eventually joined a gang of likewise corrupt ex-cops, led by former homicide detective and career criminal Frank Delano, and became Delano's number three man.

Hawaii 5-0
Jack acted mostly as a bodyguard and enforcer to Delano as he seen numerous times alongside Delano, not being far away from his employer. In the episode Ma'eme'e (episode), Delano forced Trisha Joyner to withdraw money from a bank which he believes is rightfully his. Delano was accompanied to the bank by Trisha, Kono, Jack, and Ray Mapes.

Death
The "mission" looks suspicious to the entire bank and one worker threatens to press a silent alarm button but Delano takes a worker hostage and Jack takes out his respective sidearm to quell the riot. Unbeknownst to them, both Hawaii Five-0 and the HPD are outside waiting, all while also serving as a secret back-up for Kono.

Kono revealed herself as having been undercover the whole time after kicking out Jack's gun and attempted to subdue him. Being more experienced than Kono, Jack easily subdued her and then Delano non-fatally shot her in the right shoulder. The two then fled the bank with a hostage as a shield and attempted to escape only to be surrounded by the police. Delano suddenly opened fire at the police and Jack started shooting as well.

Jack attempted to take out all the present police officers and clear a safe way for his boss but was ultimately shot dead by Detective Sergeant Danny "Danno" Williams. Delano himself was wounded by Captain Fryer and then taken into custody.

Trivia

 * He was the first senior member of Delano's crew to be killed by Detective Danny Williams