William Henry "Hank" Green II, born on May 5, 1980, is an American vlogger, science communicator, entrepreneur, author, internet producer, and musician. He is renowned for producing the YouTube channel Vlogbrothers, where he and his older brother, author John Green, regularly upload videos. Hank is also recognized for creating and hosting educational YouTube channels like Crash Course and SciShow. Additionally, he has advocated for and organized social activism, created and hosted various other YouTube channels and podcasts, released music albums, and gained a substantial following on TikTok.

Together with his brother John, Hank co-created VidCon, the world's largest conference about online videos, and the Project for Awesome, an annual online charity event, as well as the now-defunct conferences NerdCon: Stories, focused on storytelling, and PodCon, focused on podcasts. He is the co-creator of The Lizzie Bennet Diaries (2012–2013), a web series adaptation of Pride and Prejudice in the style of video blogs. He is also the co-founder of the merchandise company DFTBA Records, the crowdfunding platform Subbable, game company DFTBA Games, and online video production company Pemberley Digital, which produces video blog adaptations of classic novels in the public domain. Green is the founder of the environmental technology blog EcoGeek, which evolved into Complexly, an online video and audio production company of which he is the CEO. Green also hosts the podcasts Dear Hank & John and Delete This with his brother and wife respectively.

Green's debut novel, An Absolutely Remarkable Thing, was published on September 25, 2018; its sequel A Beautifully Foolish Endeavor was published on July 7, 2020. Both novels debuted as New York Times Best Sellers. In response to being diagnosed and treated for Hodgkin lymphoma in 2023, Green stepped down as CEO of his companies. While recovering, Green began performing stand-up about his experience. His comedy special titled Pissing Out Cancer was released on the streaming service Dropout on June 21, 2024.