McLean was born in West Palm Beach, Florida to Denise Fernandez and Bob McLean. His parents divorced and his father left the family when McLean was two, and he was raised by his mother and maternal grandparents, Ursula and Adolph Fernandez. In 1990, he moved to Orlando, Florida with his mother to concentrate on his acting and singing career. After numerous auditions for various Nickelodeon and Disney projects, he landed a role in Nickelodeon's "Welcome Freshmen" and in a comedy series called "Hi Honey! I'm Home," where he played a character named Skunk. He also won a silver medal on "GUTS" in 1992.

Rising to fame in his early teens, McLean became known as the "bad boy" of the group. In 2001, the other band members reportedly became distressed by AJ's self-destructive behavior. Following an intervention, McLean entered rehab for alcoholism and cocaine abuse. His mother, Denise McLean, later authored the book Backstreet Mom, describing AJ's life before, during, and after rehab.

In December 2003, McLean and his mother appeared on the Oprah Winfrey Show to talk about his recovery from depression, alcoholism, and drug use. Kevin Richardson, Brian Littrell, Howie Dorough and Nick Carter surprised McLean by appearing on the show to talk about their experiences with his addictions and to offer their support for his rehabilitation. This was the first time all five Backstreet Boys had appeared together in public in almost two years. His favorite musicians are James Taylor, the Dixie Chicks, America, Jimmy Buffett, and John Denver, while his favorite actors are Nathan Lane and Ben Stiller.[citation needed] The band reunited for a world tour in 2004 and released a comeback album entitled "Never Gone" on June 14, 2005.

McLean created a character, who he named Johnny No Name, to use as his alter ego. He uses it as his name when not performing with other members of the Backstreet Boys. The character has similarities to McLean; for instance, both had single mothers, and lived with their grandparents from a young age. There are also differences - Johnny has been to prison whereas AJ has not.

McLean has occasionally performed in rock/metal clubs around New York under his alter ego, Johnny No Name. He established a foundation called the JNN Foundation to raise funds for diabetes research and other causes like keeping music programs into schools.

McLean has appeared in animated show called Static Shock on the Kids WB/Cartoon Network channel as himself.

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