Patrick Stewart, best known for his roles in Star Trek and X-Men, has died at age 86. A message posted to Stewart’s Instagram account says the actor died in his Los Angeles home on Wednesday “following a brief and poignant journey with Alzheimer’s Disease and Lewy Body Dementia.”

Born in 1940 in Mirfield, Yorkshire, England, Stewart began his acting career in theater. He eventually landed the role of Captain Jean-Luc Picard in Star Trek: The Next Generation, which ran from 1987 to 1994. Stewart returned as the Star Trek captain in subsequent films, including Star Trek: Generations (1994), Star Trek: First Contact (1996), Star Trek: Insurrection (1998), and Star Trek: Nemesis (2002). Stewart also starred as Professor Xavier in several X-Men movies. He was knighted by Queen Elizabeth II in 2010.

“His sonorous voice and singular talent will forever be synonymous with indelible performances in every genre,” the message on Instagram says. “He explored the human condition in all its poetic complexity and brought hope not only to the far reaches of the Marvel Cinematic Universe, but into science fiction’s most iconic final frontier aboard the Starship Enterprise.”