This is a great and terrible loss. I've been a big fan of his for many years. Not just the films already mentioned (including one of the few redeeming qualities of The Final Frontier), but also Time After Time, The Time Bandits, Mary Poppins Returns, and, of course, Teenage Mutant Ninja Turtles II: The Secret of the Ooze. Not just films, but he was also prolific TV actor, too, with great appearances on Batman: The Animated Series, Babylon 5, Gargoyles, and Doctor Who, among many, many others.
He was truly one of the absolute finest actors to grace our screens and stages with an unforgettable voice that was perfect for audio, too. Speaking of...
Yes, you really must! Sympathy for the Devil is one of my absolute favorite Big Finish audio plays and I love that he eventually got his own ongoing series as The Unbound Third Doctor alongside Benny Summerfield. He did a number of other Big Finish audios, both Doctor Who and other properties.
Rest in peace, David Warner. Thank you for the decades of memorable characters, both good and evil.