Although he was known for being a fashion icon, he was also an actor. Most people probably recognize him as playing the antagonist "Walter Donovan" from Indiana Jones and the Last Crusade. He was the guy that "choose poorly".
Imdb says that Julian Glover played Walter Donovan.
Yep. And IMDB is correct.
Mackie acted in Hacks, Tales of the City, and The Love Boat.