SEATTLE — Washington State University is getting a $26 million donation from its richest dropout, Microsoft co-founder Paul Allen, the school said today. The gift for the university’s School for Global Animal Health was approved by the university’s Board of Regents this morning. News conferences were scheduled around the state later in the day to formally announce Allen’s gift and begin a $1 billion fundraising campaign, the largest in school history. Allen’s gift will be the largest private grant the land-grant university in Pullman has received in its 120 years — a million more than his old friend and Microsoft co-founder Bill Gates gave through his charitable foundation in 2008 to build the School for Global Animal Health, which studies diseases that move from animals to humans. In appreciation, the WSU Board of Regents voted to change the name of the school to the Paul G. Allen School for Global Animal Health. The building will also be named for Allen. Allen, 57, attended Washington State University for two years before dropping out in the 1970s to take a computer programming job. He founded Microsoft with his high school friend Gates in 1975. Allen was Microsoft’s executive vice president of research and new product development until 1983, when he left to focus on his health. Since then he has invested broadly in technology, real estate, sports and the arts. He owns the Seattle Seahawks football team and the Portland Trailblazers basketball team, and is part-owner of Seattle Sounders FC, a major league soccer team. He has a band, collects and restores vintage airplanes, and built the Experience Music Project, a museum about rock music in Seattle. Allen’s net worth totals about $13.5 billion, making him the 37th richest person in the world, according to Forbes’ September list. His charitable foundation, the Paul G. Allen Family Foundation has awarded $404 million to nonprofit organizations since 1990, primarily in the Northwest. Allen has given WSU several other smaller gifts over the years, including $195,000 in September to study the effectiveness of a technology-focused high school. In 1996, he donated $3.1 million to build a new high-tech fraternity house for his old fraternity, Phi Kappa Theta, at WSU. Ground was broken this summer for the $35 million headquarters of the School for Global Animal Health. The building was funded with a $25 million grant from the Bill and Melinda Gates Foundation. The rest came from other donors and through state bonds. The U.S. Centers for Disease Control and Prevention estimates that about 75 percent of recently emerging infectious diseases in humans are of animal origin. Among those are anthrax, HIV and mad cow.