It's easy to understand the importance of casting in a feature film, but the choice of subject for a documentary is ultimately even more critical. Fortunately, Academy Award-winning documentary filmmaker Freida Lee Mock (Maya Lin: A Strong Clear Vision) found herself a star in Wrestling With Angels: Playwright Tony Kushner, which debuted at Sundance in January 2006 and opened in limited national release on Oct. 4.

Pulitzer Prize-winning playwright Tony Kushner (Angels in America) is the star of Mock's film in every sense of the word. Seeing him speak at a college graduation shortly after reading an essay that struck her with its generosity of spirit, Mock ended up, in her own words, “stalking” him for three years. She filmed him giving humorous speeches, fretting over his weight, working on a piece about the Holocaust and, in a tremendously moving segment, getting married.

Kushner's Angels in America: A Gay Fantasia on National Themes is one of the most renowned theatrical works in history. The 1991 play won not only the Pulitzer but two Tony Awards, the New York Drama Critics Circle Award and the Los Angeles Drama Critics Circle Award. It was also selected as one of the 10 best plays of the 20th century by London's National Theatre.

The film is divided into three acts, each one taking place within a one-year period, starting with Sept. 11, 2001. Act 1, “As A Citizen of the World,” interweaves scenes from two Kushner plays with global themes. One is Only We Who Guard the Mystery Shall Be Unhappy, in which Laura Bush (Marcia Gay Harden) reads to dead Iraqi children, and the other is the critically acclaimed but controversial Homebody/Kabul.

The second act, “Mama, I'm a Homosexual Mama,” has some of the film's most powerful moments, including the speech given by Kushner's father at Kushner's wedding to Mark Harris, in which he quotes Shakespeare:

Let me not to the marriage of true minds
Admit impediments. …
If this be error and upon me proved,
I never writ, nor no man ever loved.

Act 2 also includes an interview with Kushner's father in which he examines the evolution of his acceptance of his son's homosexuality. At one point, he recalls, he told his son he wouldn't have wanted to be Tchaikovsky's father, even though the composer was a genius, because Tchaikovsky was gay. Later, tears in his eyes, he says he came to understand he was, in fact, Tchaikovsky's father, and at that point there could be no question of his pride.

Kushner's Jewish heritage and concern for political change are the focus of Act 3, “Collective Action to Overcome Injustice.” Two plays, Kushner's Caroline, or Change and the children's Holocaust opera Brundibar (for which Kushner wrote the English-language libretti), provide compelling backdrops for an examination of Kushner's activism and the role of the arts in social change.

An interview with Brundibar stage designer and illustrator of the Brundibar book, Maurice Sendak, is especially hard-hitting. Brundibar was originally written as a Nazi propaganda piece, performed by Jewish children in a concentration camp. After the film of the opera was completed, nearly all the children were killed by the Nazis. Survivor Ela Weisberger, who performed the opera 55 times as a child in the Czech concentration camp Theresiensdat, is interviewed briefly on screen, and much of the audience at the San Francisco screening of Wrestling With Angels wept during her remarks.

The documentary includes some wonderful historic footage: Meryl Streep reading Kushner's devastating prayer to God in which he doesn't ask for but demands a cure for AIDS at an AMFAR benefit in the 1990s; Kushner winning the Emmy for the miniseries version of Angels in America; excerpts and behind-the-scenes footage from the miniseries; and enormous amounts of otherwise unavailable film of Kushner's stage works.

Some reviewers have taken Mock to task for her lack of balance in her portrayal of Kushner, by which they seem to mean she doesn't have anyone criticizing him onscreen — and that's an accurate observation. Kushner is served up with a radiant glow of wit, intelligence and enormity of spirit.

But this doesn't weaken the experience of seeing the film; at no point is a viewer likely to stop and say, “Now would be a good time to say something bad about Tony.” Mock carries the audience with her during Kushner's funny speeches, his flights of fancy, his reminiscences, his family interactions, his painful moments.

Does the lack of any negative voice weaken the film as a documentary record? It's hard to detach from the power of the film itself to answer that question, but it probably does. It's also true that Kushner is — along with being passionately committed to social change and artistic achievement — intelligent, articulate and laugh-out-loud funny. There are worse problems for a film to have than for its subject to be overly fascinating.

The New York Times wrote about Kushner: “Some playwrights want to change the world. Some want to revolutionize theater. Tony Kushner is that rarity of rarities: a writer who has the promise to do both.” Never in the nearly two hours of Wrestling with Angels does Mock lose sight of the connection between both those goals in Kushner's work.

At a filmmaker's question and answer session after the screening in San Francisco last June, Mock said that the most important lesson she learned from working with Kushner was that as artists and human beings, “We have an ethical obligation to not despair.” Ultimately, Wrestling with Angels is an exercise in creativity and joyfulness of spirit, laced with moments of intense sadness and great hilarity. Mock seems to have found a way to honor that obligation.

Wrestling With Angels: Playwright Tony Kushner opens in limited national release on Oct. 4 at New York 's Film Forum. Visit wrestlingwithangelsthemovie.com for information on additional screenings.