Richard Kulinski has been discussed, but another interesting example of someone who may have become a run of the mill serial killer if they had not had the opportunity to join organized crime is
Nicky Scarfo, boss of the Philadelphia mafia during a good portion of the 80s. Scarfo was genuinely a lunatic and in the book "Blood and Honor" one of his former henchmen who became a federal informant talks about how Scarfo would get totally psyched up on violence and basically acted manic after personally killing someone. The henchmen gives an anecdote where they were just hanging out with a contractor (one of Scarfo's front companies was a cement business) and Scarfo just went and randomly shot the contractor to death because he thought the contractor insulted his business, then kept raging and seething while the guy's body was just sat there bleeding out.
Scarfo is also interesting because he should never have been near the wheels of power in the first place. Because he was a bloodthirsty manlet he tried to become a boxer but didn't have much interest outside of just the hurting people aspect. When he ultimately failed to get anywhere, he was brought into the mafia by his family members because he really couldn't function anywhere else. After he stabbed a guy to death in the middle of bar over some dumb perceived slight, Scarfo got exiled to Atlantic City, which in the 70s was just a dead backwater. Scarfo scraped by as a loan shark and low rent pimp until by dumb luck (which seems to be the theme of his life) two things happened right around the same time: 1. The long time boss of the Philadelphia mafia was assassinated and a power struggle to replace him started and 2. Atlantic City legalized gambling.
What I also find fascinating is that Scarfo had this weird ability to change the entire culture of the people around him, despite not being particularly charismatic or even intelligent. The Philadelphia mob really became a reflection of him, going from fairly low-key and professional to a bunch of coked-out cowboy nutcases that would kill people publicly or deliberately leave bodies to be found out in the open. Scarfo's end was inevitable, especially because he unhesitatingly killed anyone he though might be cooperating with police, but he more or less sealed his fate by ordering the killing of his own former mentor's son really just out of jealousy that the guy was better-liked and seemed much more competent to everyone else. Everybody eventually sold out Scarfo to the feds, including his own nephew, and he finally just died in prison a few years ago after having been locked-up for close to three decades.
For the poster that mentioned punishment for killers' families, that also sort of happened to Scarfo. His middle son followed him into organized crime, got shot at a bunch, and now is locked-up for the foreseeable rest of his life, his oldest son changed his name and completely disowned his family, and his youngest son tried to kill himself when it became clear his dad was going to jail but only succeeded in ending up in a vegetative state for about 25 years before finally dying, which sounds just absurdly nightmarish.
My personal fave: Heriberto Seda, aka the New York Zodiac Copycat. A zip gun toting tard that managed to go on for three years, with the NYPD tying itself into knots trying to catch him. Was eventually busted sevel years later, and only because he shot his sister in the ass during a nigga moment, then signed his arrest papers with the same symbol he used for his "Zodiac" letters. Everything about this case is pure lolmilk.
I think there is a criminal lolcow thread floating around somewhere that definitely needs to be revived because stories like this are great.