Over the course of two hours inside a small dressing room at the Kirk Douglas Theatre, Val Kilmer ages 20 years.

His hair turns a crazy, curly white, a strong mustache sprouts on his upper lip, and deep bags appear under his eyes. Eventually the actor is nearly unrecognizable — instead, he's Mark Twain and ready for the one-man show "Citizen Twain."

"There's a part of the makeup that starts to become the way I understand Mark Twain," says Kilmer, sitting in the makeup chair. "He's old in my story … old people are often frustrated because their movement becomes restricted."

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Kilmer later puts on a white suit and adopts a strong Southern accent. Sometimes he even sits in the audience before the show, drinking a glass of whiskey. Eventually he gets up and makes his way to the stage.

"Where am I? What year is this?" he asks.

Transformative character acting isn't uncommon for Kilmer — he played Jim Morrison in Oliver Stone's "The Doors," Doc Holliday in "Tombstone," and was Batman in the 1995 "Batman Forever."

Though he's spent the last 20 years predominantly in film, his acting career actually began onstage — at 17 he was accepted to Juilliard's drama division.

But this time, Kilmer also wrote the play and directs it.

Ten years ago Kilmer decided to write a screenplay but, stuck without the financing, he developed "Citizen Twain."

"Theater has less moving parts, and it's much less expensive to make a play than a movie," he says.

The play has at its center Mark Twain and Mary Baker Eddy, the founder of the Church of Christ, Scientist — two disparate historical icons whose lives briefly intertwined when Twain criticized Eddy in the press.

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"They're unique, self-made Americans, who both represent aspects of the American character," he says.

But in the play, Twain provides an apology to Eddy that he was never able to clearly express in real life; after all, Twain and Eddy never actually met. Eddy was a point of fascination for Twain; he even wrote a book called "Christian Science" that both flattered and criticized Eddy's work.

"He did bully her, and he was careless," says Kilmer. "She had legitimate success, and he basically practiced some pretty shoddy journalism by introducing ideas that were conveniences to him, like the accusation that she was a plagiarist."

Eddy is mentioned frequently in the play but is only a phantom character used to bring out a less-seen side of Twain.

"There are parts of his nature that perfectly represent the masculine side of our consciousness," Kilmer says, but the incorporation of Eddy brings out a feminine side, "a recognition of a different way of being strong, a feminine strength. Eddy represents that sensitivity."

Twain is only human, and this, Kilmer admits, is suggested in the title — a play on the 1941 classic film "Citizen Kane," starring Orson Welles.

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