William Henry Green II (born May 5, 1980) is an American YouTuber, science communicator, novelist, stand-up comedian, and entrepreneur. He produces the YouTube channel Vlogbrothers with his older brother, author John Green, and hosts the educational YouTube channels Crash Course and SciShow. He has 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.