Luke killed Frank Smith. Damien Smith inherited his father money and property but he became partners with Sonny to run the mob. Damien wanted the money but wanted to maintain the appearance of being a legitimate businessman. Sonny wanted the power and to take over in Port Charles.
Frank's death created a vacuum where other mob people wanted to take over his territory and thus began the merry-go- around of the numerous mobster would want Sonny's new territory and lose (Joe Scully, Moreno, Sorel, Luis Alcazar, Lorenzo Alcazar, Faith, Manny Ruiz, the Zaccaras, Joe Scully Jr and now the Jeromes).
When Lily decided she wanted to marry Sonny, her father, Hector Rivera in Puerto Rico offered to make Sonny his heir. When Hector accidentally killed Lily instead of Sonny, Sonny went to Puerto Rico to confront a sickly Hector. Sonny left a gun so Hector could kill himself and walked out of the room without confirming if he was dead. Dummy.
Sonny inherited Rivera's holdings and became even more powerful.
Meanwhile, Damien who went to the best private schools and colleges wanted to be viewed as legitimate and disassociated himself from his family's infamny. He was best friends with Ned. He ended up screwing with Bobbie's life, tried getting Lucy to sleep with him and eventually got himself killed trying to stalk his former lover Katherine Bell. Only Katherine and Ned went to his funeral and he left his fortune to Katherine.
Honestly, Fluke is probably Damien but it is sad that he would threaten to kill Ned, one of the few people that actually cared that he died. However, I can easily believe he grew to hate Sonny and want revenge since Sonny became powerful while he ended up "dead."