William Henry Green II (born May 5, 1980) is an American vlogger, science communicator, entrepreneur, author, internet producer, and musician. He is known for producing the YouTube channel Vlogbrothers with his older brother, author John Green, as well as for creating and hosting the educational YouTube channels Crash Course and SciShow. He has also advocated for and organized social activism, created and hosted a number of other YouTube channels and podcasts, released music albums, and amassed a large following on TikTok.
