In the 1982 comedy My Favorite Year, Peter O’Toole plays Allan Swann, a legendary actor who’s been booked to appear on a live TV show, but who proves to be an erratic drunk when he arrives. O’Toole was nominated for a Best Actor Oscar for playing Swann—one of a record eight times he was a nominee but not a winner—and critics raved about his performance in a part that seemed tailor-made for him. O’Toole himself was known at times to be a prodigious drinker, like so many of the other English, Irish, Scottish, and Welsh actors of his generation; like Swann, he always seemed unknowable at his core, but worth any trouble because he was so consistently capable of brilliance.

O’Toole, who died on Saturday in London, had a movie career that lasted over 50 years, with one signature role after another: T.E. Lawrence, Henry II (times two), Arthur Chipping, Jack Gurney, Eli Cross, Allan Swann, and his last major performance as an ailing actor named Maurice in the 2006 dramedy Venus. What almost all of those characters have in common is a combination of assuredness and unpredictability. They all seem to know exactly what they’re doing, even though they often baffle and exhaust everyone around them.

This quality dates back to O’Toole’s breakout role, in David Lean’s epic biopic Lawrence Of Arabia. The actor attended The Royal Academy Of Dramatic Art in the early 1950s, and went through the usual apprenticeship of doing Shakespeare at the Old Vic and appearing in TV dramas before Lean took a chance on him, casting him as the famed British Army officer and intellectual who helped shape the U.K.’s Middle East policies in the 1910s. Lean’s film depicted Lawrence as a visionary with a touch of madness about him, and O’Toole embodied that precisely, coming across as superior to the military culture that spawned Lawrence, yet also unexpectedly fragile. With his preternaturally piercing blue eyes and commanding presence, O’Toole’s Lawrence is simultaneously alien and frighteningly human.

So it goes for O’Toole in 1964’s Becket, where he’s a monarch carrying on his own private war with the church, and 1968’s The Lion In Winter, where he plays the same monarch as aged but still ornery, and 1972’s The Ruling Class, where he’s a mentally ill aristocrat convinced he’s either the Lord God or Jack The Ripper. For many movie buffs, the quintessential O’Toole role—if not Lawrence or Swann—is in Richard Rush’s 1980 cult film The Stunt Man. As the dictatorial movie director Eli Cross, O’Toole sometimes literally hovers above the fray, snapping orders to his minions from his crane, risking their lives capriciously. In all of these films, O’Toole is eccentric yet magisterial, and as eye-catching as any special effect.

O’Toole was also an excellent writer, and the two volumes of his memoir present him as personable and witty, sharing stories about his colorful upbringing in Loitering With Intent: The Child and about his RADA years in Loitering With Intent: The Apprentice. In recent years, O’Toole spoke occasionally about a third volume that would cover his entree into film, which O’Toole fans can only hope was far enough along before his death to see publication in some form. The literary O’Toole is different from the men he played onscreen, and presents a fuller picture of a man who was beloved by many of his co-stars. But even the charming O’Toole of his autobiographies and talk-show appearances maintained an air of mystery. O’Toole always seemed so much more intense than other human beings: handsomer, more in touch with his emotions, and perpetually lost in thoughts that the rest of us could never fully comprehend. There’s never been another actor quite like him, and it’s heartbreaking to think that never again will a director be able to point a camera at O’Toole and let the world marvel.