Frank Delano was a corrupt ex-cop from the Homicide Division of the Honolulu Police Department and the founder and leader of a criminal organization that consisted exclusively of corrupt former police officers. In addition to being a significant enemy to Five-0, Delano served as a primary antagonist in the early episodes of Season 2 and the premier episode of Season 3.
Little is known about Delano, except that at some point he became a police officer in the Honolulu PD and eventually rose to become a detective in Homicide. At some point, however, Delano became corrupt and eventually Vince Fryer, Delano's partner, assisted in Delano's firing from the police.
He would then form his own crew of dirty cops and be involved in a variety of other scams and crimes, including murder, money laundering etc, something which would caught the future attention of Fryer, who eventually try to bring down his former partner.
Under the orders of Captain Vince Fryer, Officer Kono Kalakaua (2010), after being "stripped" of her badge went undercover to bring down his organization.
The operation was so secretive that Kono's colleagues, Lieutenant Commander Steve McGarrett (2010), Detective Sergeant Danny Williams (2010), Agent Lori Weston and Kono's cousin, Detective Lieutenant Chin Ho Kelly (2010) were unaware of what was really going on and even began believing that Kono had gone corrupt although Fryer and Kono later told the team the truth concerning the undercover operation.
Delano was eventually arrested and jailed although in the Season 2 finale episode, Ua Hala (episode), he blackmailed Chin into freeing him from prison and later forced him to choose between Kono and his wife, Dr. Malia Waincroft.
Chin chose Malia and headed home, only to discover that she had been shot. Prior to that, Chin also contacted Kono's boyfriend, Adam Noshimuri who saved Kono from death but tragically, Malia succumbed to her wounds, leaving Chin devastated and hellbent on avenging Malia's passing.
Luckily, though, Hawaii Five-0 caught word and were on the getaway vehicle within minutes with many members of the crew dying in the gunfight that erupted between the two teams.
Delano later fled to a parking garage where he was confronted and wounded by Chin. After discovering that he has run out of bullets and seeing that Chin is tempted to shoot him despite being unarmed, Delano tells Chin that only a dirty cop, which Chin isn't, would shoot an unarmed man. Chin then responds by shooting Delano in cold-blood with his shotgun, killing the dirty ex-cop and avenging Malia's death.
Unfortunately, it was later revealed that Delano had a brother named Paul who kidnapped Chin and put him in prison in the Season 3 episode, Olelo Ho'Opa'I Make (episode) although again, thanks to Steve, Danny and Kono, Chin was saved while Paul was arrested.
Delano was a ruthless, sociopathic, opportunistic, menacing, calculating and intelligent criminal mastermind and crooked ex-cop, who showed little to no empathy for his victims and/or if anyone who gets in his way. Such a notable example of Delano's vicious sadism is how he forced Chin to release him and then forced him to make the difficult decision of choosing his wife or cousin, both of whom he already had or attempted to kill.