Brad McQuaid, the lead developer for the groundbreaking massively multiplayer online (MMO) game EverQuest, has died, according to an update from his development team. He was 51.

Details about the circumstances of his death have not been shared publicly, other than a mention that he passed away in his home. The Twitter account for Pantheon, McQuaid's project at the time of his death, and Visionary Realms, the company behind it, tweeted out the following announcement:

It is with deep regret we share that Brad McQuaid passed away last night. He will be deeply missed and forever remembered by gamers worldwide. Thank you for bringing us together through your worlds. Rest in peace @Aradune. VR offers our deepest condolences to Brad’s family.

McQuaid worked as a game programmer and designer starting back in the late 1980s, but he is most well-known for his role as lead programmer, producer, and designer (at various times) on EverQuest , the 1999 massively multiplayer online role-playing game (MMORPG) that defined the genre to this day. EQ, which adapted the DikuMUD formula from text games for a 3D persistent graphical virtual world, was a breakthrough moment for MMORPGs. Its success codified that model for the genre as other, different ideas of what MMORPGs might look like (such as those posited by Meridian 59, Underlight, or Ultima Online) largely faded into memory.

McQuaid was involved in designing some of the very first raids as we know them today, and his work had significant influence on later games like World of Warcraft, Final Fantasy XIV, The Elder Scrolls Online, Destiny, and many more.

He later went on to co-found Sigil Games, which developed and launched the hardcore MMO Vanguard: Saga of Heroes. The game found a niche audience seeking demanding, group-oriented content—a focus of McQuaid's work over the years—amidst a market of increasingly casual and solo-friendly MMOs. Most recently, McQuaid was working at Visionary Realms on the above-mentioned Pantheon, which marries that model to some newer game-design ideas. Pantheon is still in development.

Visionary Realms communications chief BenD shared these notes on the Pantheon forums:

Brad was a visionary, a mentor, an artist, a trailblazer, a friend, a husband, a father. He touched thousands of lives with his dreams and concepts. He changed the landscape of video games forever. He will be deeply missed and forever remembered in life and in Pantheon. Thank you, Brad, for bringing us together through your worlds. Rest in peace, Aradune. All of us at Visionary Realms offer our deepest condolences to Brad’s family and during this most difficult time, we kindly ask that you respect the privacy of Brad’s family.

McQuaid's passing resulted in an outpouring of mourning and memories from other notable online game developers such as Raph Koster (Ultima Online, Star Wars: Galaxies), Damion Schubert (Meridian 59, Star Wars: The Old Republic), the EVE Online team, and former Sony Online and EverQuest boss John Smedley.