Sir Ian McKellen is a great actor. We knew him for his character plays as Gandalf in Lord of The Rings and The Hobbit trilogys. Magneto in X-Men franchise. Maybe because he's too good as an actor, even when he take a break from a rehearsal, people mistaken him for a true beggar.
This happened when he step outside theater for a break after rehearsing for Waiting for Godot act. He dressed like a tramp and sat on a bench. When he opened his hat, a passer-by gave him an Australian dollar.
Source: Daily Mail