Nikos has the Master ability to control and manipulate the emotions of people. He used this ability to form a harem of beautiful/useful women that serve him zealously, committing crimes and dying for him.
Both of his runaway children have greater range with their powers than he does. His powers may have been limited to line of sight, and the effects continued even if he died. 
Regent suspected that his power gave him immunity from Nikos' power as it did his sister. This likely stems from Nikos using his power to cause his children to Trigger.
Nikos was born in Europe, later moved to Quebec. He was active for several years and never caught. He was classified as "too dangerous to fight" due to the risk of him gaining control of anyone who opposed him, human or Parahuman, as well as generally creating such volatile initial situation, that it would be borderline impossible to root it out by force without too much damage to the reputation of authorities and public morale. He was well known in North America.
↑ 1.01.11.2“If it was easy to take over a city, more people would have managed it,” I said. “This is work. There’s always more to be done, whether you’re dealing with your enemies, dealing with your subordinates or coordinating with your allies. If you find you have free time, you’re probably fucking up.”
“Or!” he said, raising a finger, “I could delegate.”
“That’s a recipe for failure,” I told him.
“My dad managed it.”
Heartbreaker, I thought. I was put in mind of the images of Heartbreaker that had made the web. The villain, by virtue of his personal, extensive harem, had a whole cadre of women virtually climbing over each other for the chance to fawn over him and worship him. The pictures were a consequence of that, released by his ‘girls’, as Regent had termed them. Each picture depicted a man in his thirties or forties, depending on the time the picture in question had been taken. He had black hair, the scruff of a beard, and was invariably seen sitting or reclining on couches and beds, often shirtless, with women at the periphery of the image. He oozed confidence and raw sexuality, languid, more lanky than athletic. - Excerpt from Imago 21.3
↑ 2.02.1‘Master’ refers to the ability to control others or (in the case of specialized cases of other powers, like Tinkers) to create minons… Taylor, Parian, Crusader, Heartbreaker and Nilbog all fit this classification.
She isn’t controlling stuffed animals the size of a second story building like Parian or directing squads of women with machine guns, grenades and zero self preservation like Heartbreaker. - Comment on Extermination 8.5
↑ 4.04.14.2I'm not saying he doesn't take what he wants. He just isn't stupid when he goes about it. He makes a lot of enemies as it stands. Cherish was frustrated that he was [abducted a starlette], and threatening to burn the rest of them. - Comment by Wildbow on Reddit
↑I looked at the rings on the memorial. “Heartbreaker’s.”
“He collected them. I uncollected them.”
“I’d heard he died.”
Imp nodded slowly. “Said I would. I told you I’d kill his dad for him.” - Excerpt from Scarab 25.6
↑ 6.06.1“And if they tried to come at me through my family, they’d get what they deserved,” Regent said.
“Why?” Parian asked.
“His dad’s Heartbreaker,” Tattletale said.
“Oh. Oh wow.”
“Funny thing is,” Regent said, “If you think about it, we might be bigger than Heartbreaker, now. People all over America know who we are, and I’m not sure if Heartbreaker is known that far to the south or west.” - Excerpt from Imago 21.1
↑Lisa whistled, “After Coil let that detail slip, I made a mental list of possibilities. Had it narrowed down to four. Heartbreaker was one, the pieces fit, but it was so hard to believe.”
“He’s big,” Brian said.
“No,” Alec shook his head, “He’s scary. He’s newsworthy. But he’s not all that.” - Excerpt from Buzz 7.1