Brian Dennehy confronts an almost-impossible part at the Taper in ‘The Steward of Christendom,’ a green monster of a play set in post-revolutionary Ireland

Brian Dennehy prepares for the physical challenge and exhausting material of the rarely performed “Steward of Christendom.” (Bob Chamberlin / Los Angeles Times / November 7, 2013)

Brian Dennehy sat cross-legged on a stool and bent to rub his aching right knee and shin. His day of rehearsing "The Steward of Christendom" would soon be done.

But the physical nicks and dings that the former Columbia University football lineman and ex-Marine copes with at age 75 weren't his main concern. He was more worried about getting his head around the part he'd handpicked for himself to play at the Mark Taper Forum, knowing full well that it's a forbidding green monster.

Green because it's Irish, Dennehy's favorite flavor by birth. Monster because Sebastian Barry's 1995 drama about the Irish Revolution of the early 1920s and its aftermath poses immense challenges of mood, memorization and storytelling. If they are not mastered, audiences are at risk of becoming lost amid the complexities of Irish history and the drifting of the protagonist's senescent mind.

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"The logical question is, 'What the hell are you doing this for?' and I haven't got an answer now," was one of the first things out of Dennehy's mouth after the rehearsal — the son of an Associated Press news editor making his interviewer's job easy. "I'm probably too old for a challenge like this. But what the hell, why not? It's a beautiful, beautiful play."

"The Steward of Christendom" takes place mainly in the memory of Thomas Dunne, a former Dublin police superintendent relegated to a mental asylum. He struggles with loneliness, dementia and the lingering weight of national and family upheaval that fell on him during the violent birth of the Irish Republic.

The play is hardly ever staged, even though it made the original Thomas, Donal McCann, the toast of the English-speaking theater world. There has never been a major, or perhaps even an amateur, production in Southern California.

"One of the reasons is that the leading role is so damn difficult," said director Steven Robman, reunited with Dennehy in a rehearsal room for the first time since 1985, when they worked on the last in a series of Irish-themed plays they'd tackled together in New York, L.A. and Chicago.

"It's a huge load, even more of a load than King Lear, given what he's charged with demonstrating. You wouldn't do it unless you felt you had to," Robman said. Dennehy will be onstage for all but a few moments of the two-hour, 15-minute play.

McCann vetoed a proposed 20-week run on Broadway in 1997, instead playing a shorter stand at the Brooklyn Academy of Music. "The starring role is so exhausting that not even McCann, who has the strength and stamina of a great athlete, could promise more than 12 weeks," Newsweek reported.

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Dennehy is committed to six weeks at the Taper, but he's the same age Barry specifies for Thomas; McCann was in his early 50s.

What's daunting, Dennehy said, is "the range of notes you're going to be playing." Inhabiting Thomas calls for humor, swagger, anguish and rage. Much of the part's poignancy resides in quietly luminous moments of inward reconciliation the actor must outwardly project.

The character has 10 long monologues, three of them extending through two full pages of a tightly printed play script.

Barry, who based the story on his own great-grandfather (it's one of many plays and novels he has mined from his family's history), is allowing some small changes to help clarify historical nuances for Americans. The play is set in 1933 and looks back on events leading up to 1922, when Irish rebels ousted the British, then fell to fighting among themselves.

Dennehy's past association with director Robman was pivotal. It brought him to the Chicago theater scene and introduced him to a crucial ally in Robert Falls, the Goodman Theatre artistic director who has cast Dennehy repeatedly in monumental roles there for more than 20 years.

From the late 1970s into the early 2000s, the actor's size and craggy, strong-jawed looks made him a go-to guy for films and TV movies in need of a bulldog lawman or a menacing sociopath. Now he jokes that he's reached an age when the pickings are much leaner, with Morgan Freeman monopolizing the good parts that do come up. "And so he should."

In "The Challenger Disaster," a new TV movie co-produced by the BBC and the Science Channel, Dennehy plays the chairman of the presidential commission investigating the 1986 space shuttle explosion, with William Hurt as the star expert witness, physicist Richard Feynman.

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While screen roles have ebbed, Dennehy has become certified over the past 15 years as one of America's elite stage actors. He won Tony Awards for best actor as Willy Loman in "Death of A Salesman," (1999) and as James Tyrone opposite Vanessa Redgrave, Philip Seymour Hoffman and Robert Sean Leonard in "Long Day's Journey Into Night" (2003), productions that began at the Goodman.