By Elizabeth Valk Long

Anybody who has read TIME in its electronic edition on America Online and ventured into our computer message boards knows Tom Mandel. For the past 1 1/2 years, he has been our online host, greeting new visitors, starting new topics, steering the discussion, arbitrating the sometimes contentious debates and teaching us-readers and journalists alike-how computers can be used to forge new and unexpected bonds between people.

But the most important lesson Tom taught was the one that began last November, when he announced online that he had been diagnosed with inoperable lung cancer. In a typically understated message, Tom bravely declared that he would enjoy what remained of his life while doing all he could "to marshal the army of good cells to enter into battle with the army of bad cells."

For the next five months, he opened his life, and his heart, to a growing legion of well-wishers -- most of whom had never met him face-to-face but who sometimes felt they knew him better than their friends in the "real" world.

He was a remarkable man. An ex-U.S. Marine. A Vietnam veteran. A Jesuit-trained polemicist with what he proudly claimed was the first college degree in futurism. In his workaday job, he was paid by SRI International to peer into the future and tell corporate clients how to prepare for the 21st century.

But it was on the computer networks that he found his true voice, first at the San Francisco-based WELL (where he posted tens of thousands of messages a year) and then at Time Online. He was a gifted writer and a fearless debater: witty, opinionated, unflinchingly open and honest. He brought all those qualities-and more-to his struggle with cancer, and they were reflected in the staggering array of get-well messages posted by his online friends.

"I am trying to figure out how to write about this experience we are all having together," he said in one posting. "In many different traditions, to be alive is to immerse oneself intensely and directly in the world. This is a new part of the human world, a brand-new social construction made up mainly of people talking to one another through keyboards and screens. Immersing myself in it even more so than I already have is part of being alive for me . and part of dying."

Tom Mandel left us last week, listening to the fourth movement of Beethoven's Ninth Symphony, the "Ode to Joy." He was 49.