L.A. Reid is moving on from Island Def Jam. The record label’s CEO and Chairman, who has been instrumental in the careers of Rihanna, Mariah Carey, Justin Bieber, and Usher, has officially announced his resignation.

In an e-mail sent to his staff on Thursday, the 54-year-old executive said that he’s optimistic about the future. “I have always thrived on growth and the next great challenge, and I look forward with much enthusiasm to what the future holds,” he wrote. “I am extremely proud of our beautiful roster and all we have accomplished in my seven years with IDJ. We continue to have incredible success together with today’s most phenomenal superstars.”

Reid is rumored to be heading over to Sony Music to assume a top executive role alongside Doug Morris, who hired him to replace Lyor Cohen at IDJ in 2004. He will also reportedly appear as a judge on the U.S. edition of Simon Cowell’s singing competition “The X Factor” this fall.

Barry Weiss will assume Reid’s position as Chairman/CEO of Island Def Jam as well as Universal Motown Republic Group. Weiss was formerly Chairman/CEO for RCA/Jive Label Group, where his roster included Justin Timberlake, Jamie Foxx, Britney Spears, Jennifer Hudson, and Ke$ha.