As a teenager in Boston, Massachusetts, Mahoney was drawn to the industry the moment he walked into a tattoo shop, describing the experience as an "epiphany."
But tattooing was illegal in Massachusetts — for health reasons; the ban was overturned in 2000 — when Mahoney first took an interest 40 years ago, so he's surprised by his own success on a mainstream scale.
"There were no books in the library. There was nothing I could find about it when I started, so this is like another planet. I didn't think this would ever be like this in my wildest dream," he said.
His rise to become a tattooist to the stars began in the 1980s when celebrities including his friend Mickey Rourke began hanging out at his tattoo shop and popularizing the look.
From there, Mahoney carved a name for himself and attracted some of the biggest stars in the world to his tattoo shop, the Shamrock Social Club, in Hollywood.
"My strong suit is that I'm a good listener. I listen to what they say and I'm of the mind that it's a joint effort, it's me and you, it's not my artwork on you, it's our artwork."