Any actor who dreams of setting the silver and small screens on fire for decades should take notes from Martin Sheen’s book.

The tempered steel he brought to his role as Capt. Willard in Apocalypse Now in 1979 and the compassionate grit he brought to his role as President Bartlet in The West Wing from 1999 to 2006 are two of several performances that have made him a household name.

Sheen’s played men with strength and inner fire, and this Friday, you’ll see exactly where he got those traits from when he’s featured in the premiere episode of season three of NBC’s genealogy series Who Do You Think You Are?

He’ll be the latest celebrity investigating his family history in the intriguing reality series that offers a unique look at the lives and backgrounds of the rich and famous.

Sheen, who had an Irish mother and a Spanish father, told the press on Monday that he traveled the world for information on his roots for the show, and he discovered that he’s got strong men on both sides of the family.

His uncle Michael on his mother’s side fought first in the Irish War of Independence and then against the Free State in the Civil War from 1921 to 1923.

Check out the preview from Martin Sheen’s appearance on Who Do You Think You Are?

And his uncle Matias on his father’s side fought against General Francisco Franco’s forces in the Spanish Civil War that began in 1936. Matias was given a life sentence in jail that was rescinded in 1969.

Sheen’s proud of the discovery. “Both of them had risen up against oppression and in one case a dictatorship in Spain and had suffered mightily for it but stuck to his principles,” he said, impressed by their courage. “Maybe this is some unknown quality that I have possessed.”

He definitely got the fighting genes. Sheen’s an activist who supported Cesar Chavez’s farm worker’s rights movement in the 1960s and signed a declaration in 2003 opposing the Iraq War. He’s also an environmentalist and opposes the genocide in Darfur.

Sheen, who’s not computer literate, accepted the offer to do Who Do You Think You Are? without hesitation when producers asked because he’d already been a fan of the show.

The decision cemented his love for his family. “They were Celtic on both sides. They were united by a peasant heritage,” Sheen said. “Both of them shared the Catholic faith and loyalty to family, community, [and] country.”

But no family’s without drama, including Sheen’s. He discovered that, on his father’s side, one of his great great great grandfathers, Don Diego Francisco Suarez, was a judge who prosecuted one of his great great great grandmothers.

“I think I said in the show that if you were to write a novel with all of these intriguing relationships so long ago, your editor would be remiss if they didn’t say, ‘No, no, this is too far-fetched. No one is ever going to believe this,’” Sheen said.

Although he’s proud of each side of his heritage, Sheen’s had to choose one over the other at least once. His birth name is Ramón Estevez, which he’s never changed, but he chose “Martin Sheen” for his stage name when he started his acting career.

“When I went to New York in 1959, I had a great deal of difficulty projecting a Spanish heritage because there was so much prejudice against Puerto Rican community,” he said. Today Puerto Ricans are integral to that region’s culture, but back then? Not so much.

The young actor was concerned about how attitudes would affect his career, so he got creative. He was a friend of Robert Dale Martin, a casting director at CBS back then, and he knew of Bishop Fulton J. Sheen, the televangelist who hosted the inspirational TV show Life is Worth Living, so he took pieces of both their names and came up with “Martin Sheen” as his professional moniker.

Racial attitudes changed by the time his children were born. He encouraged his famous sons Emilio Estevez and Charlie Sheen to keep their Spanish names. Emilio got the message, but Charlie, whose real name is Carlos Estevez, chose a stage name because he wanted to be associated with his father’s legacy.

In the elder Sheen’s opinion, his family’s journey has become a traditional American story. His ancestors sent his mother Mary Anne stateside when she was 21 to protect her from the danger of the fighting in Ireland, and she met Spaniard Francisco Estevez in her new home, whom she eventually married.

Ramón “Martin Sheen” Estevez, the son of two immigrants, was born in the United States and forged an exemplary career and legacy of achievement that’s lasted generations. Today, he hopes his appearance on Who Do You Think You Are? will instill a sense of pride and inspiration in his relatives and descendants that keeps that history of excellence going — even after he’s gone.

“I felt a sense that I was doing it for my grandchildren and their children. I felt like I had a responsibility to go to this place at this time because, you know, I am 71 years old. I don’t know how much longer I am going to be around,” he said.

And Sheen has tips for other celebrities who decide to go on the same journey he did.

“If you love adventure, strap your seat belt. And if you think you know where you are going or what you are going to see you better get ready to be surprised — and in most cases, to be very surprised and very gratified.”