Michael Gambon has played Hogwarts headmaster Albus Dumbledore for five years, but hasn't cracked a single one of the Harry Potter novels.

The choice not to read J.K. Rowling's book series, he explains, is deliberate, and he points out that co-stars Ralph Fiennes and Alan Rickman haven't taken up the books either.

"You'd get upset about all the scenes it's missing from the book, wouldn't you?" Gambon said by phone from New York, where he was promoting this week's opening of the franchise's sixth installment, "Harry Potter and the Half-Blood Prince." "No point in reading the books, because you're playing with (screenwriter) Steve Kloves' words."

And Kloves, along with director David Yates, has demanded an intense Dumbledore, who in the fourth film shook Harry when the boy wizard's name wound up in the Goblet of Fire. It's a characterization that isn't as pronounced in the book — Dumbledore doesn't yank and jostle his star student, for starters — and it upset many Potter fans.

In fact, many riled-up muggles also took to the Internet after the third film to complain that Gambon doesn't have the same kindly grandfather aura they came to expect in the books and in the first two films (when the role was portrayed by the late Richard Harris).

Since joining the cast in the third movie, "Harry Potter and the Prisoner of Azkaban," Gambon has fashioned Dumbledore into a tougher patriarch, an urgent and mysterious force in the midst of impending war.

Less cuddly, this Dumbledore is clearly presented as a formidable opponent to Potter's snake-faced nemesis, Voldemort.

While Harris (who died in London at age 72 in 2002) had a twinkling gentleness, Gambon's Dumbledore is a wry observer with crackling wit.

"He's got to be a bit scary," the 68-year-old Irish actor said of his Dumbledore. "All headmasters should be a bit scary, shouldn't they? A top wizard like him would be intimidating. And ultimately, he's protecting Harry. Essentially, I play myself. A little Irish, a little scary. That's what I'm like in real life."

The actor says the enormity of the "Potter" phenomenon hit him again recently at the London premiere of "Half-Blood Prince," where more than 4,000 kids turned up to get a glimpse of the magical cast. Gambon called it both heartwarming and bittersweet.

"I was really moved by the number of children there. It was raining and everyone was drenched, some of them had been there for hours. You feel responsible for them in a way. All their books and pieces of paper for autographs were all wet, the pens wouldn't work. It was so sad. It makes you realize how big this thing is."

The filming of the final Harry Potter movies, the two-part "Harry Potter and the Deathly Hallows," is under way but Gambon's scenes aren't scheduled until February.

He says that makes it feel as if the end is still far away for him, but he has already begun to reflect on the experience.

"It's been," he said, "a real privilege."

Watching stars Daniel Radcliffe, Emma Watson and Rupert Grint grow up has been especially fun. "They've become worldly, wise and strong actors. That's been nice to see. You can say things to them now that you couldn't say to them then."

Like what? "Oh, I don't know. I dare not say," he said, chuckling. Should we assume the worst? "Yes," he answered with cryptic sass. How very Dumbledore.