Rapper, producer, and Anticon co-founder Brendon “Alias” Whitney died of a heart attack on Friday, according to an announcement his friend and collaborator Sage Francis made on Twitter Saturday afternoon. He was 41 years old.

Saturday, Anticon’s official Twitter feed also posted a confirmation of Whitney’s passing.

In 1996, Whitney joined fellow rapper Sole’s Live Poets outfit, which was later rechristened as Deep Puddle Dynamics. While recording under his moniker Alias, Whitney co-founded the experimental indie label Anticon in 1998 along with Doseone, Odd Nosdam, Yoni Wolf, and Sole.

Following an Anticon catalog of studio projects dating back to 1998’s Anticon Presents: Hip-Hop Music For The Advanced Listener, Alias’ friends and industry peers took to Twitter with condolences.

Whitney released upwards of a dozen studio projects under the stage name Alias, including 2002’s The Other Side of the Looking Glass. His most recent full-length solo project was 2014’s Pitch Black Prism.