As a celebrity in the public eye, Sean Penn has always come off as a little stuffy and rigid. He's a full-throated liberal, yes, but he also has exhibited in interviews and at awards functions that his sense of humor—or lack thereof—leaves something to be desired. This, of course, has nothing to do with the actor side of Penn, whose quarter-century-plus career has been laden with performances both over-the-top (2003's "Mystic River," 2006's "All the King's Men") and brilliant (1995's "Dead Man Walking," 2001's "I Am Sam"). Playing the real-life Harvey Milk, the first openly gay man elected into major U.S. political office, Penn is nothing less than transformative in the aptly-titled biopic "Milk." This is one of those watermark turns that an actor waits all their life to play, and he disappears into the role with every fiber of his being.

Set in the eight-year period between 1970 and 1978, Harvey Milk (Sean Penn) meets the much younger Scott Smith (James Franco) on the eve of his fortieth birthday, and the two of them embark on a long, solid relationship together. At the time, Harvey was just a Wall Street businessman, not yet out of the closet. Needing a fresh start in a place where they can reinvent themselves, Harvey and Scott move to downtown Castro Street in the heart of San Francisco and open up a camera shop. In a time when gay people's Civil Rights were still being fought, this portion of the Bay Area becomes something of a mecca for a minority no longer wanting to live their lives in the shadows. Rallying the cause is Harvey himself, who comes to run for office on the city's Board of Supervisors. It takes him three tries, but he finally succeeds at getting elected just as the fight against Proposition 6, which would take away the rights of gay men and women to be school teachers, heats up.

In direct opposition of Harvey on the matter of Prop. 6 is fellow board supervisor Dan White (Josh Brolin), a staunch Republican whose refusal to vote alongside Harvey seems to be less about his own beliefs and more about his fear of what those colleagues and family members might think if he supported the homosexual cause. When Harvey says at one point, "I think Dan might be one of us," it is merely unsubstantiated hearsay that could very well be the truth. Whatever the case may be, it was at the hands of Dan White, bitter over his terminated position after he quit, that both Mayor George Moscone (Victor Garber) and Harvey Milk were shot to death at City Hall on November 27, 1978. Harvey, who always believed he wouldn't live to see fifty, was forty-eight years old, and had been in office eleven months.

"Milk" is directed by Gus Van Sant, a brave cinematic trailblazer whose last four motion pictures—2002's "Gerry," 2003's "Elephant," 2005's "Last Days," and 2008's "Paranoid Park"—have been ponderous, powerful avante garde mood pieces about as far away from the Hollywood mainstream as one could get. His creative juices satiated but not diffused, Van Sant returns to a more conventional storytelling mindframe with "Milk," but smartly opts to avoid anything that might be considered manipulative or mawkish. The film is not without a couple contrivances, such as a warm telephone conversation Harvey Milk has with ex-lover Scott Smith on the morning of his murder, but these are few and far between.

The dramatic weight that builds as "Milk" presses forward, then, comes from its gritty, unsentimental portrait of a man who inspired a segment of the country's population to look beyond their timeworn prejudices and toward a future where, as the Declaration of Independence states, "all men are created equal." On a mission to tear down stereotypes, Harvey also made it seem okay for gay people to come out of the closet and embrace who they truly are. By the supremely touching conclusion, as Scott Smith and Harvey's dedicated campaign manager Anne Kronenberg (Alison Pill) stumble onto the street outside City Hall to see thousands of people, lit candles in hand, marching along in dedication to Harvey, the film has earned its emotional catharsis. It is a wonderful moment, devastating and uplifting at once.

Sean Penn deserves all the accolades sure to be bestowed upon him for his portrayal of Harvey Milk. He is surrounded by a first-class ensemble, no one hogging the spotlight but everyone making an impression. James Franco (2008's "Pineapple Express") is excellent as Scott Smith, sweetly underplaying the part of a man who loves Harvey, but is unprepared for the tireless activist his longtime boyfriend becomes. As lesbian campaign manager Anne Kronenberg, Alison Pill (2007's "Dan in Real Life") is confident and lovely, blowing into the film at the halfway point like a force to be reckoned with. Emile Hirsch (2008's "Speed Racer") brings welcome layers and shading to valued assistant and promoter Cleve Jones, a character who might have looked underwritten on the script page.

Diego Luna (2004's "The Terminal") has a less firm grip on his role as Jack Lira, whom Harvey takes up with after Scott leaves him. Is Jack an alcoholic? Manic-depressive? And what does Harvey see in him? Their relationship feels a bit half-formed. One actor who has no trouble reading his character is Josh Brolin (2008's "W."), superb as board supervisor Dan White. Though White ultimately was the assassin behind Harvey's death, he is not treated as a villain, but as a multidimensional person who struggles and finally gives up finding a common ground between himself and Harvey. Brolin keeps his calm and is all the more chilling because of it, particularly in later scenes where doom imminently hangs over the proceedings.

Tech credits are unshowy and perfectly realized, from the cinematography by Van Sant regular Harris Savides, to the costume and production designs, to the soundtrack and music score by Danny Elfman (2006's "Charlotte's Web"). The film looks, sounds and feels like the 1970s, rather than a fictional representation of the time period. "Milk" is all the more timely in that it is being released in November 2008, thirty years beyond its setting and with California's Proposition 8 ban against gay marriage near the forefront of many people's consciences. Though a lot has changed for the better since 1978, it is sobering to realize that the fight for tolerance and gay rights in America is far from over. With every two steps forward, it seems like the country takes one step back. It is due in part to Harvey Milk's work and legacy that that first step was taken at all.