PASADENA, Calif. -- Viewers of HBO's "The Pacific" may or may not recognize actor Joe Mazzello, but odds are good they've seen him before: At age 9, he starred as the grandson of the founder of "Jurassic Park" in that 1993 hit movie, directed by Steven Spielberg, who is also an executive producer on "The Pacific."

Now 26, Mr. Mazzello is back on screen as Marine Eugene Sledge in "The Pacific."

Where has he been since the 1997 "Jurassic Park" sequel? Growing up.

"I always lived in upstate New York, and my parents kept me grounded," he said after an HBO press conference in January. "I had a very normal life. I'd play kickball and play in the leaves and then I'd go off to these exotic locations [to make a movie]."

Mr. Mazzello said he went three years without an agent or manager, and he attended film school at the University of Southern California so he could "learn more about Mr. Spielberg's profession."

Mr. Mazzello said he's never taken acting classes -- "it's something that just came naturally to me" -- and despite his past association with Mr. Spielberg on the first two "Jurassic" films he had to audition six times for "The Pacific."

"I wasn't going to get a $200 million favor from us working together 15 years ago," Mr. Mazzello said, referencing the reported budget for the entire miniseries.

Making "The Pacific" has been a three-year journey for the actor, who will appear in the fall movie "The Social Network" about the creation of the website Facebook. Mr. Mazzello spent 10 months filming "The Pacific" in Australia. He said the combination of physical and emotional demands made the role a challenge.

"Every day you'd go home, take a shower, eat a club sandwich and go to bed," he said, "because you needed as much sleep as you could get for how physical it was."

Mr. Mazzello was one of several cast members who had grandfathers who served in World War II.

"Everything about making this and doing this is exhausting ... but it's so worth it having the personal connection with my grandfather. We lost him while I was filming. He knew I was doing it and felt so proud, and I felt so honored to be able to honor men like him. Like a lot of veterans, he would try to change the subject a bit. He would always talk about the wisecracks and good times with his buddies, the nice moments of companionship. He didn't talk too much about his Purple Heart, but he certainly was very affected by [the war]."

After landing the role, Mr. Mazzello said he read "With the Old Breed," Mr. Sledge's account of his World War II experience. He was struck by the bluntness of how Mr. Sledge described the conditions.

"It was very matter of fact just in the telling," Mr. Mazzello said. "I'd have to put the book down every once in a while because I was so affected by how nonchalantly he talked about these horrible things he had to go through. But it was his job, and you felt that sense of duty and honor just coming out of the pages."

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