Patrick Stewart, the British actor who played Captain Jean-Luc Picard in Star Trek: The Next Generation, has died at 86. A statement posted Thursday on his Instagram account said he died the previous day at his home in Los Angeles, with his wife, Sunny, by his side. The statement also said Stewart had Alzheimer’s disease and Lewy body dementia.

Stewart’s portrayal of Picard became one of his defining roles. With a measured manner and commanding presence, he played the Enterprise captain as a diplomat whose crew followed his lead. Star Trek: The Next Generation ran from 1987 to 1994, setting its story roughly a century after the original series.

Stewart was not initially the look the show’s creator, Gene Roddenberry, had imagined for the new captain. The actor auditioned wearing a toupee sent from London, but executives saw him both with and without it and chose his bald appearance.

After The Next Generation, Stewart continued playing leaders on screen, taking the role of Professor Charles Xavier in the X-Men films. He portrayed the telepathic mutant across multiple movies over 17 years, often appearing alongside his longtime friend Ian McKellen. Earlier in his career, Stewart worked on the British stage with the Royal Shakespeare Company and received numerous acting awards.

William Shatner, who played Captain James T. Kirk in the original Star Trek, remembered Stewart as a friend and colleague, praising the intelligence, grace and humanity he brought to his roles. Shatner wrote that Picard represented “the best of us.” George Takei and Wil Wheaton also paid tribute, with Wheaton, who played Wesley Crusher on The Next Generation, sharing a photo of the two and writing, “Godspeed, Captain.”

Stewart is survived by Sunny and his two children. In a 2009 Guardian essay, he wrote candidly about witnessing violence by his father against his mother and the lasting impact of his childhood.

Sources: CNET.