Billionaire Paul Allen has taken his friend Bill Gates up on his challenge to publicly pledge the majority of his wealth to philanthropy.

TED S. WARREN/ASSOCIATED PRESS

Paul G. Allen, owner of the Seattle Seahawks, attends a Seahawks game in Seattle in December. Allen was undergoing treatment for non-Hodgkin's lymphoma.

Allen, who is 57, said today that he plans to leave the majority of his $13 billion estate to philanthropy to continue the work of his foundation and to fund scientific research. It was also a way of marking the 20th anniversary of the Paul G. Allen Family Foundation, which he started in 1990 with his sister, Jo Lynn Allen, and has since given 3,000 grants totaling about $400 million.

A month ago, Bill and Melinda Gates and Warren Buffett began a public campaign to encourage other billionaires to make a "Giving Pledge," and donate at least half of their wealth to charity.

Allen said he has planned to do that for many years, but he had not gone public with his intentions until now.

"He and Bill have talked about this and he thinks it's a good idea to let people know," said David Postman, a spokesman for Allen at Vulcan. "He hopes that maybe it spurs other people to give and he's hoping there will be good things that come of it."

Allen said he wanted to make it clear that his philanthropic efforts "will continue after my lifetime," he said in a statement. "As our philanthropy continues in the years ahead, we will look for new opportunities to make a difference in the lives of future generations."

This year Forbes ranked Allen as the world's 37th richest person with a fortune estimated at $13.5 billion.

His total giving over the years has reached about $1 billion, reflecting eclectic interests in science, the arts and education, including nonprofits he founded: the Allen Institute for Brain Science and the Experience Music Project.

While Gates' charity has become global in size and ambition, Allen's has remained mostly local and personal.

"Since the beginning, our philanthropy has been focused in the Pacific Northwest, where I live and work," Allen said. "I'm proud to have helped fund great work done by non-profit groups throughout the region. But there's always more to do."

Allen has battled non-Hodgkin's lymphoma since his diagnosis last fall. He has finished chemotherapy treatments and has been been doing well, Postman said. Allen traveled to Africa recently, and has been "running businesses as much as he ever has. He stays intimately involved in the things he cares about."

JIM HALLAS/AP PHOTO/EASTSIDE JOURNAL

Microsoft founders and future billionaires Bill Gates, left, and Paul Allen in Bellevue in 1981, when the company employed less than 100 people.

The Paul G. Allen Family Foundation also announced $3.9 million in funding to 41 nonprofit organizations in the Pacific Northwest, focused largely on arts and culture.

The foundation gave Anniversary grants of $20,000 each to five individual founders of nonprofits, recognized as "change agents who created organizations that continue to deliver high impact programs for local communities."

The recipients are Rachel Bristol, founder and CEO of Oregon Food Bank; Bridget Cooke, founder and executive director of Adelante Mujeres in Forest Grove, Ore.; Jeanne Harmon, founder and executive director of the Center for Strengthening the Teaching Profession in Tacoma; Myra Platt and Jane Jones, founders of Book-It Repertory Theatre in Seattle; and Ken Stuart, founder and president of Seattle Biomedical Research Institute.