"Poppy" is a character portrayed by Moriah Pereira.
The Poppy YouTube channel was created back in October 6, 2011 but her first video was uploaded November 9, 2014, titled 'Poppy Eats Cotton Candy', which only shows Poppy eating cotton candy, as the title says. The most popular video of Poppy is 'I'm Poppy', which shows Poppy saying "I'm Poppy" multiple times for 10 minutes. This video is actually the same 3-4 minute clip, but repeated. The channel's subscriber count is hidden, but was accidentally shown as of June 4th 2017 to have 639k subscribers.
The videos are directed by Titanic Sinclair, who worked with a different woman (Mars Argo) in the past before working with Moriah. The videos are meant to be a mock of today's pop culture.
Many YouTubers, such as PewDiePie or LeafyIsHere, have made videos about Poppy commenting about how strange her channel was. Night Mind, a channel posting videos explaining different kinds of horror/creepy content, created a video explaining of whom Poppy was. Another channel, Joe the UFO, has a series of videos talking about some of Poppy's content.
Poppy's Twitter was created on January 2011 but her first tweet was posted the same day her first YouTube video was posted. The tweet advertises the video. Her twitter account has 150K followers so far, Her Instagram's account's creation date is unknown but her first post suggests the same thing. The account has 573k followers so far.