Books: Gary Sinise’s memoir isn’t your typical celebrity dispatch. Then again, he’s not your typical actor.

When he was a sophomore in high school almost a half-century ago, three words changed Gary Sinise’s life: “Come and audition.” As he relates in his new memoir, “Grateful American,” those words came from Barbara Patterson, the formidable drama department head at Highland Park High School outside Chicago where the performing arts were as much a priority as sports.

Up to that point, Sinise had been an indifferent student who played in a rock band. Rebellious, he frequented the school’s “Glass Hallway,” a corridor notorious as the hangout of the school’s longhairs, slackers and stoners. Patterson, casting “West Side Story,” thought Sinise would make a good gang member.

And just like that, Sinise’s life was transformed. “I found this new place that felt like home,” the actor said during a recent phone interview.

Fresh out of high school, he co-founded the Tony-winning Steppenwolf Theatre Company. It initially operated on a shoestring in a Highland Park church basement. Now, 45 years later, it occupies its own multimillion-dollar facility in Chicago’s Lincoln Park. Meanwhile, Sinise became a celebrated fixture on screen: He won an Emmy for his lead role in the TV biopic “George Wallace” and played haunted Gulf War vet and detective Mac Taylor for nine seasons on “CSI: NY.” But he’s best known as the grievously injured and psychologically scarred Lt. Dan in “Forrest Gump,” a role that earned him an Oscar nomination but also steered his life into one devoted to service. Patterson may have sealed Sinise’s fate, but the 1994 drama gave his life meaning in a new way.

“Grateful American” isn’t your typical navel-gazing celebrity dispatch. The plain-spoken, Midwest-grounded Sinise has always been about the work and not the fame, so he resisted prodding by his agents and managers to write a memoir. When he decided it was time, he determined that instead of a chronicle of his Glass Hallway-to-stardom journey, he would reflect on a life enriched by “blessings, gratitude and giving back,” he said.

He chose an incident from his first play to set the stage for these themes.

During “West Side Story’s” first curtain call, Sinise, a supporting player, was pulled from the back of the stage by one of the show’s leads, Jeff Melvoin, to take his bows upfront with the show’s stars. “I don’t know why he did that, or if he would even remember,” Sinise said of Melvoin, who went on to become the Emmy-winning writer and producer of “Northern Exposure.” “It meant so much to me.”

What Melvoin does “vividly” remember is that “Gary was beloved by everybody,” he recalled during a phone conversation.

“He became the heartbeat of the production,” Melvoin said. “We all knew how much the show meant to Gary, and it would have been just a very natural thing to recognize this person who we cared for so much for his passion.”

“Grateful American” is the story of how Sinise felt compelled to redirect that passion on behalf of American troops, wounded veterans and first responders and their families.

In 2011, he created the Gary Sinise Foundation, which raised $35 million last year. Among its programs is the construction of specially adapted smart homes for severely wounded veterans that are provided mortgage-free. Sinise also leads the Lt. Dan Band, which has performed hundreds of shows on concert stages, at military bases and in war zones. Sinise writes that he hopes the book inspires readers to “overcome obstacles, embrace gratitude and engage in service above self.”

The book does contain some startling personal admissions, including a harrowing section about his wife, actress Moira Harris, and her struggles with alcoholism. “I was not going to include it in the book unless she was supportive of that,” he said. But out of that darkness, the family found their faith and their church, and Harris told her husband that she hoped this difficult chapter might help somebody going through a similar situation.

Sinise’s connection to and appreciation of the military preceded his portrayal of Lt. Dan. His grandfather fought on the front lines at the Battle of the Argonne Forest in France in World War I. One of his uncles flew 30 missions over Europe as a navigator aboard a B-17 bomber during World War II. Another served on a U.S. Navy ship. His father was a Navy photographer during the Korean War. Sinise himself was conceived on a naval base, he noted.

Sinise came of age during the Vietnam War era, but given his family’s military service, he was not caught up in anti-war sentiment. Any protests he attended in high school were a dodge to get out of class.

“If you could prove you went to a moratorium, the teachers would be OK with it,” he said with a laugh.

When Steppenwolf was established, he mounted plays such as “Tracers” that portrayed the reality and psychology of the Vietnam experience. He also instituted veterans’ nights at the theater, offering free admission to those who served (this program is still in practice).

The tragedy of 9/11 was the “terrible catalyst” that galvanized his commitment to the military, he said. When visiting hospitals and war zones, “a few people might know who Gary Sinise is, but everybody has seen ‘Forrest Gump’ and knew who Lt. Dan was,” he said. “I’d walk into a hospital room with a guy missing his arms and legs and he’d want to talk about Lt. Dan.”

That character suffers physically and emotionally after he loses his legs in combat. But by the end of the movie, “he is married, in a successful business and back up on his legs,” Sinise said. “He is moving on with his life. That was a story not often seen on screen, and that’s what I’m devoting my life to right now; trying to provide hopeful support.”

At a time when even performing at the Super Bowl has become politicized, Sinise pointedly does not talk politics either in the book or in an interview. Although he’s known as one of few conservatives in Hollywood – and he contributed money to the campaigns of the late senator John McCain, which also aligned with his pro-veteran mission, and Mitt Romney – he says he feels strongly that politics has no place when it comes to supporting the troops. This attitude was influenced by the ill treatment many soldiers from Vietnam received when they returned from that unpopular war.

He’s more interested in unifying messages, and if “Grateful American” has one it’s the recurring phrase “I can do more.” Over the past 40 years, Sinise has received several humanitarian awards as well as the Presidential Citizens Medal, the second highest honor the president can bestow on a civilian, but he’s far from done growing the foundation to expand its impact and support.

“The more I did, the more I felt I could do and the more I wanted to do,” he said. “God pointed me in this direction and said you’ve had a lot of success; do some good with it.”