Dan Mahoney, also known as Dennis N. Griffin, was born on September 21, 1947, in New York City. He was the eldest of five children, with three sisters named Peggy, Kathy, and Pat, and a brother named Eddie. After graduating from high school at the age of sixteen, Mahoney worked for a year as an auto mechanic and machinist before enlisting in the Marines at seventeen. He later served in Vietnam as a machine gunner with the 9th Marines, an outfit known as The Walking Dead.
After being discharged from the Marines in 1968, Mahoney joined the NYPD, where he worked for twenty years in various patrol and detective commands. During this time, he also took advantage of the VA Bill and attended John Jay College of Criminal Justice part-time, eventually graduating with a BA in Romance Languages in 1977. Mahoney also worked as Yoko Ono's security chief after John Lennon's murder, a job that allowed him to travel to some very nice places.
In 1989, Mahoney retired from the NYPD and began working as the director of investigations for the Holmes Detective Bureau, a well-regarded New York PI agency. He also started working on his first book, Detective First Grade, which was published in May 1993 and received good reviews. Since then, Mahoney has written seven more books, all featuring Detective Brian McKenna or Detective Cisco Sanchez as the protagonist. His books have received good reviews and have sold well, with all of them still in print. Mahoney now works for the Department of Homeland Security but plans to retire soon to focus on his writing. His hobbies include skiing, traveling, and socializing with his friends in pubs, where they often reminisce about their old cases.