Its director, David France, was out of town, and so the three Act Up alumni, all of whom appear in the film, substituted for him, answering questions and meeting attendees. The room was packed, and Mr. Cox, 44, was in particularly fine form, lapping up the attention and eager to talk about where the battle needed to go next.

Without a doubt, there had been changes in Mr. Cox's physical appearance over the years. He had lipodystrophy, a form of fat redistribution common in long-term H.I.V. patients, giving them sunken cheekbones and distended bellies — not to mention severe vision problems caused by an infection called CMV retinitis.

Still, Mr. Staley recalled: "He was great. He was dynamic. He was speaking about what AIDS activists need to be looking at now, with rising H.I.V. infection rates among young gay men. He was as insightful as he'd always been."

But just a few weeks later, on Dec. 18, Mr. Staley found himself standing in a hospital, listening as doctors told him that Mr. Cox had died from AIDS-related causes, a result, apparently, of going off his medications. Afterward, on The Huffington Post and other Web sites, a furious debate ensued about just what Mr. Cox's death represented.

Was it "pill fatigue," a term applied to patients who grow exhausted taking a variety of medications daily and then become noncompliant? Why would Mr. Cox devote his life to obtaining lifesaving medications for people all over the world, only to stop taking them himself?

Was Mr. Cox trying to kill himself after several years in which the side effects had been nearly as bad as the disease? Or could crystal meth have been to blame?

The answer may be more complicated than any of them acknowledged.

SPENCER COX WAS BORN in Atlanta on March 10, 1968, and grew up there with his younger brother, Nick, and his mother, Beverly, a certified public accountant. His father drank too much, and mostly disappeared from the picture around the time Spencer was 5.

As a child, Mr. Cox devoured books by Chaucer and Dickens and immersed himself in local theater. He came out early in high school, said his mother, who described it as being not such a big deal. "I said to a friend: 'Would I prefer a child with a wife and two children and white picket fence? Sure. But I didn't have that choice,' " she said. "And I don't think he had problems in high school."

In 1986, Mr. Cox left the South for Bennington College in Vermont, where he studied theater and introduced his friends to Bette Davis movies, which he could recount line for line. Then, after spending much of his junior year in New York and becoming involved with Act Up, the famously combative AIDS organization founded by the playwright Larry Kramer, Mr. Cox dropped out of Bennington and moved to Manhattan.

In short order, he found out he was H.I.V. positive. Bodies were piling up all around him.

"He had a tough and scary road ahead of him," said John Voelcker, a friend from the old days who was with Mr. Cox the day he was tested. "AIDS was not then a chronic, manageable disease. It was something that killed."

But after wiping away his tears, Mr. Cox threw himself back into his work at Act Up, where he served on the treatment and data committee. And in 1995, when protease inhibitors were in the testing phase, Mr. Cox (who had never taken any real interest in science before becoming involved in AIDS issues) played an integral role in helping to speed along and design the trial process for the drug Norvir.

"He was brilliant," Mr. Kramer said. "He figured out single-handedly how to test these drugs more effectively than any scientist and statistician could."

It helped save the lives of thousands of people, including himself.

Yet as the medications began to work, the movement itself — the organizing principle in Mr. Cox's life — splintered, then broke down. An ever-escalating real estate market made it far more difficult for creative types, including those who toiled away on AIDS issues, to survive in New York City. The clubs and bars where Mr. Cox and his Act Up compatriots spent their nights — Woody's, Boy Bar, Mars — closed their doors, and the Internet became a prevalent way for gay men to socialize and hook up.

All of this came with clear psychological and physical costs, particularly as crystal meth moved into the gay party scene. Many of the most prominent AIDS activists spiraled downward. Dr. Gabriel Torres, who ran the AIDS ward at St. Vincent's Hospital in Greenwich Village, fell into a decade-long battle with addiction, winding up in and out of jail. Rodger McFarlane, the former executive director at Gay Men's Health Crisis, committed suicide. Peter Staley developed a meth habit in 2002, before rehabilitating himself.

To Mr. Kramer, it was a horrible if somewhat predictable development.