William (known as Bill) is a professor of ecology at Oregon State University, known for his research on the role of the grey wolf as an apex predator and a keystone species. Bill is director of the Alliance of World Scientists, a group of over 25,000 scientists concerned about climate change.

He was lead author on the 'Global Scientists' Warning to Humanity: A second Notice', published in 2017 with 15,364 scientist co-signatories from 184 countries. In 2020, he led The World Scientists' Warning of a Climate Emergency signed by 11,000 scientists who declared: "Planet Earth is facing a climate emergency". He continues to publish new 'Scientists’ Warning' papers.