Ian McKellen (character)

Sir Ian McKellen is a famous English actor. His career spans four decades. The Simpsons met McKellen when they were visiting England.

History
McKellen was starring in the play  and was standing outside the theater when the Simpsons came walking by. After they exchanged greetings, McKellen said he had a show to do, and said that in the theatrical world, the custom was to not mention the name of the play in which he was appearing, in order to avoid bad luck. Homer, seeing the play's name on the marquee, innocently asked, "Macbeth?" and a car drove through a nearby puddle, drenching McKellen from head to toe. McKellen said "You fool! You've doomed us all!" Homer, oblivious to what was causing the bad luck, asked "By saying Macbeth?" and an anvil fell out of the sky and landed on McKellen's foot.

A round of conversation ensued, during which everyone (including McKellen) said "Macbeth" at least once, and each time someone said the name of the play, McKellen was struck by a bolt of lightning:
 * As McKellen hopped on one foot after the anvil fell on him, Homer asked what was bad luck to say. McKellen exasperatedly replied "Macbeth!" Then McKellen realized what he'd done, and the first bolt of lightning hit him.
 * Bart, seeing an opportunity for mischief, deliberately said the play's name three times in succession, and McKellen was quickly zapped by three lightning bolts.
 * Marge told Bart to "Stop saying Macbeth!" and McKellen was hit by yet another lightning bolt.
 * Lisa, shocked, told Marge that she'd said "Macbeth", and McKellen was struck yet again.
 * Homer, trying to make up for what had happened, apologized to "Mr. Macbeth", and McKellen was hit by another lightning bolt.

McKellen, replying to Homer's apology, said that it was all right because they didn't know. He then excused himself, saying he had a performance to give. The Simpsons wished him good luck. McKellen, aghast, said that was also bad luck, and a large piece of the theater marquee promptly fell on him.

Behind the Laughter

 * The conversation about Macbeth, during which McKellen is repeatedly struck by lightning, is a reference to the about mentioning the play's name being bad luck.
 * There is also a superstition in which wishing someone "good luck" before a performance will bring them bad luck. Among actors and musicians, the custom is to instead say "" when wishing a performer good luck.