William Henry Green II is an American YouTuber, science communicator, novelist, 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.

Vlogbrothers is a video blog channel on YouTube. The Internet-based show is created and hosted by the Green brothers: John Green and Hank Green. The first incarnation of the brothers' online broadcasting was the "Brotherhood 2.0" project, preceding the establishment of the pair's regular vlogging activity through the Vlogbrothers channel.